@article{14553, abstract = {Quantum state tomography is an essential component of modern quantum technology. In application to continuous-variable harmonic-oscillator systems, such as the electromagnetic field, existing tomography methods typically reconstruct the state in discrete bases, and are hence limited to states with relatively low amplitudes and energies. Here, we overcome this limitation by utilizing a feed-forward neural network to obtain the density matrix directly in the continuous position basis. An important benefit of our approach is the ability to choose specific regions in the phase space for detailed reconstruction. This results in a relatively slow scaling of the amount of resources required for the reconstruction with the state amplitude, and hence allows us to dramatically increase the range of amplitudes accessible with our method.}, author = {Fedotova, Ekaterina and Kuznetsov, Nikolai and Tiunov, Egor and Ulanov, A. E. and Lvovsky, A. I.}, issn = {2469-9934}, journal = {Physical Review A}, number = {4}, publisher = {American Physical Society}, title = {{Continuous-variable quantum tomography of high-amplitude states}}, doi = {10.1103/PhysRevA.108.042430}, volume = {108}, year = {2023}, } @article{13227, abstract = {Currently available quantum processors are dominated by noise, which severely limits their applicability and motivates the search for new physical qubit encodings. In this work, we introduce the inductively shunted transmon, a weakly flux-tunable superconducting qubit that offers charge offset protection for all levels and a 20-fold reduction in flux dispersion compared to the state-of-the-art resulting in a constant coherence over a full flux quantum. The parabolic confinement provided by the inductive shunt as well as the linearity of the geometric superinductor facilitates a high-power readout that resolves quantum jumps with a fidelity and QND-ness of >90% and without the need for a Josephson parametric amplifier. Moreover, the device reveals quantum tunneling physics between the two prepared fluxon ground states with a measured average decay time of up to 3.5 h. In the future, fast time-domain control of the transition matrix elements could offer a new path forward to also achieve full qubit control in the decay-protected fluxon basis.}, author = {Hassani, Farid and Peruzzo, Matilda and Kapoor, Lucky and Trioni, Andrea and Zemlicka, Martin and Fink, Johannes M}, issn = {2041-1723}, journal = {Nature Communications}, publisher = {Springer Nature}, title = {{Inductively shunted transmons exhibit noise insensitive plasmon states and a fluxon decay exceeding 3 hours}}, doi = {10.1038/s41467-023-39656-2}, volume = {14}, year = {2023}, } @inproceedings{14872, abstract = {We entangled microwave and optical photons for the first time as verified by a measured two-mode vacuum squeezing of 0.7 dB. This electro-optic entanglement is the key resource needed to connect cryogenic quantum circuits.}, author = {Sahu, Rishabh and Qiu, Liu and Hease, William J and Arnold, Georg M and Minoguchi, Yuri and Rabl, Peter and Fink, Johannes M}, booktitle = {Frontiers in Optics + Laser Science 2023}, isbn = {9781957171296}, location = {Tacoma, WA, United States}, publisher = {Optica Publishing Group}, title = {{Entangling microwaves and telecom wavelength light}}, doi = {10.1364/ls.2023.lm1f.3}, year = {2023}, } @article{14032, abstract = {Arrays of Josephson junctions are governed by a competition between superconductivity and repulsive Coulomb interactions, and are expected to exhibit diverging low-temperature resistance when interactions exceed a critical level. Here we report a study of the transport and microwave response of Josephson arrays with interactions exceeding this level. Contrary to expectations, we observe that the array resistance drops dramatically as the temperature is decreased—reminiscent of superconducting behaviour—and then saturates at low temperature. Applying a magnetic field, we eventually observe a transition to a highly resistive regime. These observations can be understood within a theoretical picture that accounts for the effect of thermal fluctuations on the insulating phase. On the basis of the agreement between experiment and theory, we suggest that apparent superconductivity in our Josephson arrays arises from melting the zero-temperature insulator.}, author = {Mukhopadhyay, Soham and Senior, Jorden L and Saez Mollejo, Jaime and Puglia, Denise and Zemlicka, Martin and Fink, Johannes M and Higginbotham, Andrew P}, issn = {1745-2481}, journal = {Nature Physics}, keywords = {General Physics and Astronomy}, pages = {1630--1635}, publisher = {Springer Nature}, title = {{Superconductivity from a melted insulator in Josephson junction arrays}}, doi = {10.1038/s41567-023-02161-w}, volume = {19}, year = {2023}, } @article{14489, abstract = {Microwave-optics entanglement is a vital component for building hybrid quantum networks. Here, a new mechanism for preparing stationary entanglement between microwave and optical cavity fields in a cavity optomagnomechanical system is proposed. It consists of a magnon mode in a ferrimagnetic crystal that couples directly to a microwave cavity mode via the magnetic dipole interaction and indirectly to an optical cavity through the deformation displacement of the crystal. The mechanical displacement is induced by the magnetostrictive force and coupled to the optical cavity via radiation pressure. Both the opto- and magnomechanical couplings are dispersive. Magnon–phonon entanglement is created via magnomechanical parametric down-conversion, which is further distributed to optical and microwave photons via simultaneous optomechanical beamsplitter interaction and electromagnonic state-swap interaction, yielding stationary microwave-optics entanglement. The microwave-optics entanglement is robust against thermal noise, which will find broad potential applications in quantum networks and quantum information processing with hybrid quantum systems.}, author = {Fan, Zhi Yuan and Qiu, Liu and Gröblacher, Simon and Li, Jie}, issn = {1863-8899}, journal = {Laser and Photonics Reviews}, number = {12}, publisher = {Wiley}, title = {{Microwave-optics entanglement via cavity optomagnomechanics}}, doi = {10.1002/lpor.202200866}, volume = {17}, year = {2023}, } @inproceedings{12088, abstract = {We present a quantum-enabled microwave-telecom interface with bidirectional conversion efficiencies up to 15% and added input noise quanta as low as 0.16. Moreover, we observe evidence for electro-optic laser cooling and vacuum amplification.}, author = {Sahu, Rishabh and Hease, William J and Rueda Sanchez, Alfredo R and Arnold, Georg M and Qiu, Liu and Fink, Johannes M}, booktitle = {Conference on Lasers and Electro-Optics}, isbn = {9781557528209}, location = {San Jose, CA, United States}, publisher = {Optica Publishing Group}, title = {{Realizing a quantum-enabled interconnect between microwave and telecom light}}, doi = {10.1364/CLEO_QELS.2022.FW4D.4}, year = {2022}, } @article{10924, abstract = {Solid-state microwave systems offer strong interactions for fast quantum logic and sensing but photons at telecom wavelength are the ideal choice for high-density low-loss quantum interconnects. A general-purpose interface that can make use of single photon effects requires < 1 input noise quanta, which has remained elusive due to either low efficiency or pump induced heating. Here we demonstrate coherent electro-optic modulation on nanosecond-timescales with only 0.16+0.02−0.01 microwave input noise photons with a total bidirectional transduction efficiency of 8.7% (or up to 15% with 0.41+0.02−0.02), as required for near-term heralded quantum network protocols. The use of short and high-power optical pump pulses also enables near-unity cooperativity of the electro-optic interaction leading to an internal pure conversion efficiency of up to 99.5%. Together with the low mode occupancy this provides evidence for electro-optic laser cooling and vacuum amplification as predicted a decade ago.}, author = {Sahu, Rishabh and Hease, William J and Rueda Sanchez, Alfredo R and Arnold, Georg M and Qiu, Liu and Fink, Johannes M}, issn = {20411723}, journal = {Nature Communications}, publisher = {Springer Nature}, title = {{Quantum-enabled operation of a microwave-optical interface}}, doi = {10.1038/s41467-022-28924-2}, volume = {13}, year = {2022}, } @article{10940, abstract = {Magnetic-field-resilient superconducting circuits enable sensing applications and hybrid quantum computing architectures involving spin or topological qubits and electromechanical elements, as well as studying flux noise and quasiparticle loss. We investigate the effect of in-plane magnetic fields up to 1 T on the spectrum and coherence times of thin-film three-dimensional aluminum transmons. Using a copper cavity, unaffected by strong magnetic fields, we can probe solely the effect of magnetic fields on the transmons. We present data on a single-junction and a superconducting-quantum-interference-device (SQUID) transmon that are cooled down in the same cavity. As expected, the transmon frequencies decrease with increasing field, due to suppression of the superconducting gap and a geometric Fraunhofer-like contribution. Nevertheless, the thin-film transmons show strong magnetic field resilience: both transmons display microsecond coherence up to at least 0.65 T, and T1 remains above 1μs over the entire measurable range. SQUID spectroscopy is feasible up to 1 T, the limit of our magnet. We conclude that thin-film aluminum Josephson junctions are suitable hardware for superconducting circuits in the high-magnetic-field regime.}, author = {Krause, J. and Dickel, C. and Vaal, E. and Vielmetter, M. and Feng, J. and Bounds, R. and Catelani, G. and Fink, Johannes M and Ando, Yoichi}, issn = {2331-7019}, journal = {Physical Review Applied}, number = {3}, publisher = {American Physical Society}, title = {{Magnetic field resilience of three-dimensional transmons with thin-film Al/AlOx/Al Josephson junctions approaching 1 T}}, doi = {10.1103/PhysRevApplied.17.034032}, volume = {17}, year = {2022}, } @article{11353, abstract = {Micro- and nanoscale optical or microwave cavities are used in a wide range of classical applications and quantum science experiments, ranging from precision measurements, laser technologies to quantum control of mechanical motion. The dissipative photon loss via absorption, present to some extent in any optical cavity, is known to introduce thermo-optical effects and thereby impose fundamental limits on precision measurements. Here, we theoretically and experimentally reveal that such dissipative photon absorption can result in quantum feedback via in-loop field detection of the absorbed optical field, leading to the intracavity field fluctuations to be squashed or antisquashed. A closed-loop dissipative quantum feedback to the cavity field arises. Strikingly, this modifies the optical cavity susceptibility in coherent response measurements (capable of both increasing or decreasing the bare cavity linewidth) and causes excess noise and correlations in incoherent interferometric optomechanical measurements using a cavity, that is parametrically coupled to a mechanical oscillator. We experimentally observe such unanticipated dissipative dynamics in optomechanical spectroscopy of sideband-cooled optomechanical crystal cavitiess at both cryogenic temperature (approximately 8 K) and ambient conditions. The dissipative feedback introduces effective modifications to the optical cavity linewidth and the optomechanical scattering rate and gives rise to excess imprecision noise in the interferometric quantum measurement of mechanical motion. Such dissipative feedback differs fundamentally from a quantum nondemolition feedback, e.g., optical Kerr squeezing. The dissipative feedback itself always results in an antisqueezed out-of-loop optical field, while it can enhance the coexisting Kerr squeezing under certain conditions. Our result applies to cavity spectroscopy in both optical and superconducting microwave cavities, and equally applies to any dissipative feedback mechanism of different bandwidth inside the cavity. It has wide-ranging implications for future dissipation engineering, such as dissipation enhanced sideband cooling and Kerr squeezing, quantum frequency conversion, and nonreciprocity in photonic systems.}, author = {Qiu, Liu and Huang, Guanhao and Shomroni, Itay and Pan, Jiahe and Seidler, Paul and Kippenberg, Tobias J.}, issn = {26913399}, journal = {PRX Quantum}, number = {2}, publisher = {American Physical Society}, title = {{Dissipative quantum feedback in measurements using a parametrically coupled microcavity}}, doi = {10.1103/PRXQuantum.3.020309}, volume = {3}, year = {2022}, } @article{11417, abstract = {Over the past few years, the field of quantum information science has seen tremendous progress toward realizing large-scale quantum computers. With demonstrations of quantum computers outperforming classical computers for a select range of problems,1–3 we have finally entered the noisy, intermediate-scale quantum (NISQ) computing era. While the quantum computers of today are technological marvels, they are not yet error corrected, and it is unclear whether any system will scale beyond a few hundred logical qubits without significant changes to architecture and control schemes. Today's quantum systems are analogous to the ENIAC (Electronic Numerical Integrator And Computer) and EDVAC (Electronic Discrete Variable Automatic Computer) systems of the 1940s, which ran on vacuum tubes. These machines were built on a solid, nominally scalable architecture and when they were developed, nobody could have predicted the development of the transistor and the impact of the resulting semiconductor industry. Simply put, the computers of today are nothing like the early computers of the 1940s. We believe that the qubits of future fault-tolerant quantum systems will look quite different from the qubits of the NISQ machines in operation today. This Special Topic issue is devoted to new and emerging quantum systems with a focus on enabling technologies that can eventually lead to the quantum analog to the transistor. We have solicited both research4–18 and perspective articles19–21 to discuss new and emerging qubit systems with a focus on novel materials, encodings, and architectures. We are proud to present a collection that touches on a wide range of technologies including superconductors,7–13,21 semiconductors,15–17,19 and individual atomic qubits.18 }, author = {Sigillito, Anthony J. and Covey, Jacob P. and Fink, Johannes M and Petersson, Karl and Preble, Stefan}, issn = {0003-6951}, journal = {Applied Physics Letters}, number = {19}, publisher = {American Institute of Physics}, title = {{Emerging qubit systems: Guest editorial}}, doi = {10.1063/5.0097339}, volume = {120}, year = {2022}, } @article{11591, abstract = {We investigate the deterministic generation and distribution of entanglement in large quantum networks by driving distant qubits with the output fields of a nondegenerate parametric amplifier. In this setting, the amplifier produces a continuous Gaussian two-mode squeezed state, which acts as a quantum-correlated reservoir for the qubits and relaxes them into a highly entangled steady state. Here we are interested in the maximal amount of entanglement and the optimal entanglement generation rates that can be achieved with this scheme under realistic conditions taking, in particular, the finite amplifier bandwidth, waveguide losses, and propagation delays into account. By combining exact numerical simulations of the full network with approximate analytic results, we predict the optimal working point for the amplifier and the corresponding qubit-qubit entanglement under various conditions. Our findings show that this passive conversion of Gaussian into discrete-variable entanglement offers a robust and experimentally very attractive approach for operating large optical, microwave, or hybrid quantum networks, for which efficient parametric amplifiers are currently developed.}, author = {Agustí, J. and Minoguchi, Y. and Fink, Johannes M and Rabl, P.}, issn = {2469-9934}, journal = {Physical Review A}, number = {6}, publisher = {American Physical Society}, title = {{Long-distance distribution of qubit-qubit entanglement using Gaussian-correlated photonic beams}}, doi = {10.1103/PhysRevA.105.062454}, volume = {105}, year = {2022}, } @misc{14520, abstract = {This dataset comprises all data shown in the figures of the submitted article "Compact vacuum gap transmon qubits: Selective and sensitive probes for superconductor surface losses" at arxiv.org/abs/2206.14104. Additional raw data are available from the corresponding author on reasonable request.}, author = {Zemlicka, Martin and Redchenko, Elena and Peruzzo, Matilda and Hassani, Farid and Trioni, Andrea and Barzanjeh, Shabir and Fink, Johannes M}, publisher = {Zenodo}, title = {{Compact vacuum gap transmon qubits: Selective and sensitive probes for superconductor surface losses}}, doi = {10.5281/ZENODO.8408897}, year = {2022}, } @phdthesis{12366, abstract = {Recent substantial advances in the feld of superconducting circuits have shown its potential as a leading platform for future quantum computing. In contrast to classical computers based on bits that are represented by a single binary value, 0 or 1, quantum bits (or qubits) can be in a superposition of both. Thus, quantum computers can store and handle more information at the same time and a quantum advantage has already been demonstrated for two types of computational tasks. Rapid progress in academic and industry labs accelerates the development of superconducting processors which may soon fnd applications in complex computations, chemical simulations, cryptography, and optimization. Now that these machines are scaled up to tackle such problems the questions of qubit interconnects and networks becomes very relevant. How to route signals on-chip between diferent processor components? What is the most efcient way to entangle qubits? And how to then send and process entangled signals between distant cryostats hosting superconducting processors? In this thesis, we are looking for solutions to these problems by studying the collective behavior of superconducting qubit ensembles. We frst demonstrate on-demand tunable directional scattering of microwave photons from a pair of qubits in a waveguide. Such a device can route microwave photons on-chip with a high diode efciency. Then we focus on studying ultra-strong coupling regimes between light (microwave photons) and matter (superconducting qubits), a regime that could be promising for extremely fast multi-qubit entanglement generation. Finally, we show coherent pulse storage and periodic revivals in a fve qubit ensemble strongly coupled to a resonator. Such a reconfgurable storage device could be used as part of a quantum repeater that is needed for longer-distance quantum communication. The achieved high degree of control over multi-qubit ensembles highlights not only the beautiful physics of circuit quantum electrodynamics, it also represents the frst step toward new quantum simulation and communication methods, and certain techniques may also fnd applications in future superconducting quantum computing hardware. }, author = {Redchenko, Elena}, isbn = {978-3-99078-024-4}, issn = {2663-337X}, pages = {168}, publisher = {Institute of Science and Technology Austria}, title = {{Controllable states of superconducting Qubit ensembles}}, doi = {10.15479/at:ista:12132}, year = {2022}, } @misc{10645, abstract = {Superconducting qubits have emerged as a highly versatile and useful platform for quantum technological applications [1]. Bluefors and Zurich Instruments have supported the growth of this field from the 2010s onwards by providing well-engineered and reliable measurement infrastructure [2]– [6]. Having a long and stable qubit lifetime is a critical system property. Therefore, considerable effort has already gone into measuring qubit energy-relaxation timescales and their fluctuations, see Refs. [7]–[10] among others. Accurately extracting the statistics of a quantum device requires users to perform time consuming measurements. One measurement challenge is that the detection of the state-dependent response of a superconducting resonator due to a dispersively-coupled qubit requires an inherently low signal level. Consequently, measurements must be performed using a microwave probe that contains only a few microwave photons. Improving the signal-to-noise ratio (SNR) by using near-quantum limited parametric amplifiers as well as the use of optimized signal processing enabled by efficient room temperature instrumentation help to reduce measurement time. An empirical observation for fixed frequency transmons from recent literature is that as the energy-relaxation time 𝑇𝑇1 increases, so do its natural temporal fluctuations [7], [10]. This necessitates many repeated measurements to understand the statistics (see for example, Ref. [10]). In addition, as state-of-the-art qubits increase in lifetime, longer measurement times are expected to obtain accurate statistics. As described below, the scaling of the widths of the qubit energy-relaxation distributions also reveal clues about the origin of the energy-relaxation.}, author = {Simbierowicz, Slawomir and Shi, Chunyan and Collodo, Michele and Kirste, Moritz and Hassani, Farid and Fink, Johannes M and Bylander, Jonas and Perez Lozano, Daniel and Lake, Russell}, keywords = {Application note}, pages = {8}, publisher = {Bluefors Oy}, title = {{Qubit energy-relaxation statistics in the Bluefors quantum measurement system}}, year = {2021}, } @misc{10644, abstract = {The purpose of this application note is to demonstrate a working example of a superconducting qubit measurement in a Bluefors cryostat using the Keysight quantum control hardware. Our motivation is twofold. First, we provide pre-qualification data that the Bluefors cryostat, including filtering and wiring, can support long-lived qubits. Second, we demonstrate that the Keysight system (controlled using Labber) provides a straightforward solution to perform these characterization measurements. This document is intended as a brief guide for starting an experimental platform for testing superconducting qubits. The setup described here is an immediate jumping off point for a suite of applications including testing quantum logical gates, quantum optics with microwaves, or even using the qubit itself as a sensitive probe of local electromagnetic fields. Qubit measurements rely on high performance of both the physical sample environment and the measurement electronics. An overview of the cryogenic system is shown in Figure 1, and an overview of the integration between the electronics and cryostat (including wiring details) is shown in Figure 2.}, author = {Lake, Russell and Simbierowicz, Slawomir and Krantz, Philip and Hassani, Farid and Fink, Johannes M}, keywords = {Application note}, pages = {9}, publisher = {Bluefors Oy}, title = {{The Bluefors dilution refrigerator as an integrated quantum measurement system}}, year = {2021}, } @article{9242, abstract = {In the recent years important experimental advances in resonant electro-optic modulators as high-efficiency sources for coherent frequency combs and as devices for quantum information transfer have been realized, where strong optical and microwave mode coupling were achieved. These features suggest electro-optic-based devices as candidates for entangled optical frequency comb sources. In the present work, I study the generation of entangled optical frequency combs in millimeter-sized resonant electro-optic modulators. These devices profit from the experimentally proven advantages such as nearly constant optical free spectral ranges over several gigahertz, and high optical and microwave quality factors. The generation of frequency multiplexed quantum channels with spectral bandwidth in the MHz range for conservative parameter values paves the way towards novel uses in long-distance hybrid quantum networks, quantum key distribution, enhanced optical metrology, and quantum computing.}, author = {Rueda Sanchez, Alfredo R}, issn = {2469-9934}, journal = {Physical Review A}, number = {2}, publisher = {American Physical Society}, title = {{Frequency-multiplexed hybrid optical entangled source based on the Pockels effect}}, doi = {10.1103/PhysRevA.103.023708}, volume = {103}, year = {2021}, } @misc{13057, abstract = {This dataset comprises all data shown in the figures of the submitted article "Geometric superinductance qubits: Controlling phase delocalization across a single Josephson junction". Additional raw data are available from the corresponding author on reasonable request.}, author = {Peruzzo, Matilda and Hassani, Farid and Szep, Grisha and Trioni, Andrea and Redchenko, Elena and Zemlicka, Martin and Fink, Johannes M}, publisher = {Zenodo}, title = {{Geometric superinductance qubits: Controlling phase delocalization across a single Josephson junction}}, doi = {10.5281/ZENODO.5592103}, year = {2021}, } @article{9928, abstract = {There are two elementary superconducting qubit types that derive directly from the quantum harmonic oscillator. In one, the inductor is replaced by a nonlinear Josephson junction to realize the widely used charge qubits with a compact phase variable and a discrete charge wave function. In the other, the junction is added in parallel, which gives rise to an extended phase variable, continuous wave functions, and a rich energy-level structure due to the loop topology. While the corresponding rf superconducting quantum interference device Hamiltonian was introduced as a quadratic quasi-one-dimensional potential approximation to describe the fluxonium qubit implemented with long Josephson-junction arrays, in this work we implement it directly using a linear superinductor formed by a single uninterrupted aluminum wire. We present a large variety of qubits, all stemming from the same circuit but with drastically different characteristic energy scales. This includes flux and fluxonium qubits but also the recently introduced quasicharge qubit with strongly enhanced zero-point phase fluctuations and a heavily suppressed flux dispersion. The use of a geometric inductor results in high reproducibility of the inductive energy as guaranteed by top-down lithography—a key ingredient for intrinsically protected superconducting qubits.}, author = {Peruzzo, Matilda and Hassani, Farid and Szep, Gregory and Trioni, Andrea and Redchenko, Elena and Zemlicka, Martin and Fink, Johannes M}, issn = {2691-3399}, journal = {PRX Quantum}, keywords = {quantum physics, mesoscale and nanoscale physics}, number = {4}, pages = {040341}, publisher = {American Physical Society}, title = {{Geometric superinductance qubits: Controlling phase delocalization across a single Josephson junction}}, doi = {10.1103/PRXQuantum.2.040341}, volume = {2}, year = {2021}, } @phdthesis{9920, abstract = {This work is concerned with two fascinating circuit quantum electrodynamics components, the Josephson junction and the geometric superinductor, and the interesting experiments that can be done by combining the two. The Josephson junction has revolutionized the field of superconducting circuits as a non-linear dissipation-less circuit element and is used in almost all superconducting qubit implementations since the 90s. On the other hand, the superinductor is a relatively new circuit element introduced as a key component of the fluxonium qubit in 2009. This is an inductor with characteristic impedance larger than the resistance quantum and self-resonance frequency in the GHz regime. The combination of these two elements can occur in two fundamental ways: in parallel and in series. When connected in parallel the two create the fluxonium qubit, a loop with large inductance and a rich energy spectrum reliant on quantum tunneling. On the other hand placing the two elements in series aids with the measurement of the IV curve of a single Josephson junction in a high impedance environment. In this limit theory predicts that the junction will behave as its dual element: the phase-slip junction. While the Josephson junction acts as a non-linear inductor the phase-slip junction has the behavior of a non-linear capacitance and can be used to measure new Josephson junction phenomena, namely Coulomb blockade of Cooper pairs and phase-locked Bloch oscillations. The latter experiment allows for a direct link between frequency and current which is an elusive connection in quantum metrology. This work introduces the geometric superinductor, a superconducting circuit element where the high inductance is due to the geometry rather than the material properties of the superconductor, realized from a highly miniaturized superconducting planar coil. These structures will be described and characterized as resonators and qubit inductors and progress towards the measurement of phase-locked Bloch oscillations will be presented.}, author = {Peruzzo, Matilda}, isbn = {978-3-99078-013-8}, issn = {2663-337X}, keywords = {quantum computing, superinductor, quantum metrology}, pages = {149}, publisher = {Institute of Science and Technology Austria}, title = {{Geometric superinductors and their applications in circuit quantum electrodynamics}}, doi = {10.15479/at:ista:9920}, year = {2021}, } @article{9815, abstract = {The quantum bits (qubits) on which superconducting quantum computers are based have energy scales corresponding to photons with GHz frequencies. The energy of photons in the gigahertz domain is too low to allow transmission through the noisy room-temperature environment, where the signal would be lost in thermal noise. Optical photons, on the other hand, have much higher energies, and signals can be detected using highly efficient single-photon detectors. Transduction from microwave to optical frequencies is therefore a potential enabling technology for quantum devices. However, in such a device the optical pump can be a source of thermal noise and thus degrade the fidelity; the similarity of input microwave state to the output optical state. In order to investigate the magnitude of this effect we model the sub-Kelvin thermal behavior of an electro-optic transducer based on a lithium niobate whispering gallery mode resonator. We find that there is an optimum power level for a continuous pump, whilst pulsed operation of the pump increases the fidelity of the conversion.}, author = {Mobassem, Sonia and Lambert, Nicholas J. and Rueda Sanchez, Alfredo R and Fink, Johannes M and Leuchs, Gerd and Schwefel, Harald G.L.}, issn = {2058-9565}, journal = {Quantum Science and Technology}, number = {4}, publisher = {IOP Publishing}, title = {{Thermal noise in electro-optic devices at cryogenic temperatures}}, doi = {10.1088/2058-9565/ac0f36}, volume = {6}, year = {2021}, } @article{8038, abstract = {Microelectromechanical systems and integrated photonics provide the basis for many reliable and compact circuit elements in modern communication systems. Electro-opto-mechanical devices are currently one of the leading approaches to realize ultra-sensitive, low-loss transducers for an emerging quantum information technology. Here we present an on-chip microwave frequency converter based on a planar aluminum on silicon nitride platform that is compatible with slot-mode coupled photonic crystal cavities. We show efficient frequency conversion between two propagating microwave modes mediated by the radiation pressure interaction with a metalized dielectric nanobeam oscillator. We achieve bidirectional coherent conversion with a total device efficiency of up to ~60%, a dynamic range of 2 × 10^9 photons/s and an instantaneous bandwidth of up to 1.7 kHz. A high fidelity quantum state transfer would be possible if the drive dependent output noise of currently ~14 photons s^−1 Hz^−1 is further reduced. Such a silicon nitride based transducer is in situ reconfigurable and could be used for on-chip classical and quantum signal routing and filtering, both for microwave and hybrid microwave-optical applications.}, author = {Fink, Johannes M and Kalaee, M. and Norte, R. and Pitanti, A. and Painter, O.}, issn = {20589565}, journal = {Quantum Science and Technology}, number = {3}, publisher = {IOP Publishing}, title = {{Efficient microwave frequency conversion mediated by a photonics compatible silicon nitride nanobeam oscillator}}, doi = {10.1088/2058-9565/ab8dce}, volume = {5}, year = {2020}, } @article{8529, abstract = {Practical quantum networks require low-loss and noise-resilient optical interconnects as well as non-Gaussian resources for entanglement distillation and distributed quantum computation. The latter could be provided by superconducting circuits but existing solutions to interface the microwave and optical domains lack either scalability or efficiency, and in most cases the conversion noise is not known. In this work we utilize the unique opportunities of silicon photonics, cavity optomechanics and superconducting circuits to demonstrate a fully integrated, coherent transducer interfacing the microwave X and the telecom S bands with a total (internal) bidirectional transduction efficiency of 1.2% (135%) at millikelvin temperatures. The coupling relies solely on the radiation pressure interaction mediated by the femtometer-scale motion of two silicon nanobeams reaching a Vπ as low as 16 μV for sub-nanowatt pump powers. Without the associated optomechanical gain, we achieve a total (internal) pure conversion efficiency of up to 0.019% (1.6%), relevant for future noise-free operation on this qubit-compatible platform.}, author = {Arnold, Georg M and Wulf, Matthias and Barzanjeh, Shabir and Redchenko, Elena and Rueda Sanchez, Alfredo R and Hease, William J and Hassani, Farid and Fink, Johannes M}, issn = {2041-1723}, journal = {Nature Communications}, keywords = {General Biochemistry, Genetics and Molecular Biology, General Physics and Astronomy, General Chemistry}, publisher = {Springer Nature}, title = {{Converting microwave and telecom photons with a silicon photonic nanomechanical interface}}, doi = {10.1038/s41467-020-18269-z}, volume = {11}, year = {2020}, } @misc{13056, abstract = {This datasets comprises all data shown in plots of the submitted article "Converting microwave and telecom photons with a silicon photonic nanomechanical interface". Additional raw data are available from the corresponding author on reasonable request.}, author = {Arnold, Georg M and Wulf, Matthias and Barzanjeh, Shabir and Redchenko, Elena and Rueda Sanchez, Alfredo R and Hease, William J and Hassani, Farid and Fink, Johannes M}, publisher = {Zenodo}, title = {{Converting microwave and telecom photons with a silicon photonic nanomechanical interface}}, doi = {10.5281/ZENODO.3961561}, year = {2020}, } @misc{13070, abstract = {This dataset comprises all data shown in the figures of the submitted article "Surpassing the resistance quantum with a geometric superinductor". Additional raw data are available from the corresponding author on reasonable request.}, author = {Peruzzo, Matilda and Trioni, Andrea and Hassani, Farid and Zemlicka, Martin and Fink, Johannes M}, publisher = {Zenodo}, title = {{Surpassing the resistance quantum with a geometric superinductor}}, doi = {10.5281/ZENODO.4052882}, year = {2020}, } @article{8944, abstract = {Superconductor insulator transition in transverse magnetic field is studied in the highly disordered MoC film with the product of the Fermi momentum and the mean free path kF*l close to unity. Surprisingly, the Zeeman paramagnetic effects dominate over orbital coupling on both sides of the transition. In superconducting state it is evidenced by a high upper critical magnetic field 𝐵𝑐2, by its square root dependence on temperature, as well as by the Zeeman splitting of the quasiparticle density of states (DOS) measured by scanning tunneling microscopy. At 𝐵𝑐2 a logarithmic anomaly in DOS is observed. This anomaly is further enhanced in increasing magnetic field, which is explained by the Zeeman splitting of the Altshuler-Aronov DOS driving the system into a more insulating or resistive state. Spin dependent Altshuler-Aronov correction is also needed to explain the transport behavior above 𝐵𝑐2.}, author = {Zemlicka, Martin and Kopčík, M. and Szabó, P. and Samuely, T. and Kačmarčík, J. and Neilinger, P. and Grajcar, M. and Samuely, P.}, issn = {24699969}, journal = {Physical Review B}, number = {18}, publisher = {American Physical Society}, title = {{Zeeman-driven superconductor-insulator transition in strongly disordered MoC films: Scanning tunneling microscopy and transport studies in a transverse magnetic field}}, doi = {10.1103/PhysRevB.102.180508}, volume = {102}, year = {2020}, } @article{7910, abstract = {Quantum illumination uses entangled signal-idler photon pairs to boost the detection efficiency of low-reflectivity objects in environments with bright thermal noise. Its advantage is particularly evident at low signal powers, a promising feature for applications such as noninvasive biomedical scanning or low-power short-range radar. Here, we experimentally investigate the concept of quantum illumination at microwave frequencies. We generate entangled fields to illuminate a room-temperature object at a distance of 1 m in a free-space detection setup. We implement a digital phase-conjugate receiver based on linear quadrature measurements that outperforms a symmetric classical noise radar in the same conditions, despite the entanglement-breaking signal path. Starting from experimental data, we also simulate the case of perfect idler photon number detection, which results in a quantum advantage compared with the relative classical benchmark. Our results highlight the opportunities and challenges in the way toward a first room-temperature application of microwave quantum circuits.}, author = {Barzanjeh, Shabir and Pirandola, S. and Vitali, D and Fink, Johannes M}, issn = {23752548}, journal = {Science Advances}, number = {19}, publisher = {AAAS}, title = {{Microwave quantum illumination using a digital receiver}}, doi = {10.1126/sciadv.abb0451}, volume = {6}, year = {2020}, } @inproceedings{9001, abstract = {Quantum illumination is a sensing technique that employs entangled signal-idler beams to improve the detection efficiency of low-reflectivity objects in environments with large thermal noise. The advantage over classical strategies is evident at low signal brightness, a feature which could make the protocol an ideal prototype for non-invasive scanning or low-power short-range radar. Here we experimentally investigate the concept of quantum illumination at microwave frequencies, by generating entangled fields using a Josephson parametric converter which are then amplified to illuminate a room-temperature object at a distance of 1 meter. Starting from experimental data, we simulate the case of perfect idler photon number detection, which results in a quantum advantage compared to the relative classical benchmark. Our results highlight the opportunities and challenges on the way towards a first room-temperature application of microwave quantum circuits.}, author = {Barzanjeh, Shabir and Pirandola, Stefano and Vitali, David and Fink, Johannes M}, booktitle = {IEEE National Radar Conference - Proceedings}, isbn = {9781728189420}, issn = {1097-5659}, location = {Florence, Italy}, number = {9}, publisher = {IEEE}, title = {{Microwave quantum illumination with a digital phase-conjugated receiver}}, doi = {10.1109/RadarConf2043947.2020.9266397}, volume = {2020}, year = {2020}, } @article{9114, abstract = {Microwave photonics lends the advantages of fiber optics to electronic sensing and communication systems. In contrast to nonlinear optics, electro-optic devices so far require classical modulation fields whose variance is dominated by electronic or thermal noise rather than quantum fluctuations. Here we demonstrate bidirectional single-sideband conversion of X band microwave to C band telecom light with a microwave mode occupancy as low as 0.025 ± 0.005 and an added output noise of less than or equal to 0.074 photons. This is facilitated by radiative cooling and a triply resonant ultra-low-loss transducer operating at millikelvin temperatures. The high bandwidth of 10.7 MHz and total (internal) photon conversion efficiency of 0.03% (0.67%) combined with the extremely slow heating rate of 1.1 added output noise photons per second for the highest available pump power of 1.48 mW puts near-unity efficiency pulsed quantum transduction within reach. Together with the non-Gaussian resources of superconducting qubits this might provide the practical foundation to extend the range and scope of current quantum networks in analogy to electrical repeaters in classical fiber optic communication.}, author = {Hease, William J and Rueda Sanchez, Alfredo R and Sahu, Rishabh and Wulf, Matthias and Arnold, Georg M and Schwefel, Harald G.L. and Fink, Johannes M}, issn = {2691-3399}, journal = {PRX Quantum}, number = {2}, publisher = {American Physical Society}, title = {{Bidirectional electro-optic wavelength conversion in the quantum ground state}}, doi = {10.1103/prxquantum.1.020315}, volume = {1}, year = {2020}, } @article{9194, abstract = {Quantum transduction, the process of converting quantum signals from one form of energy to another, is an important area of quantum science and technology. The present perspective article reviews quantum transduction between microwave and optical photons, an area that has recently seen a lot of activity and progress because of its relevance for connecting superconducting quantum processors over long distances, among other applications. Our review covers the leading approaches to achieving such transduction, with an emphasis on those based on atomic ensembles, opto-electro-mechanics, and electro-optics. We briefly discuss relevant metrics from the point of view of different applications, as well as challenges for the future.}, author = {Lauk, Nikolai and Sinclair, Neil and Barzanjeh, Shabir and Covey, Jacob P and Saffman, Mark and Spiropulu, Maria and Simon, Christoph}, issn = {2058-9565}, journal = {Quantum Science and Technology}, number = {2}, publisher = {IOP Publishing}, title = {{Perspectives on quantum transduction}}, doi = {10.1088/2058-9565/ab788a}, volume = {5}, year = {2020}, } @misc{13071, abstract = {This dataset comprises all data shown in the plots of the main part of the submitted article "Bidirectional Electro-Optic Wavelength Conversion in the Quantum Ground State". Additional raw data are available from the corresponding author on reasonable request.}, author = {Hease, William J and Rueda Sanchez, Alfredo R and Sahu, Rishabh and Wulf, Matthias and Arnold, Georg M and Schwefel, Harald and Fink, Johannes M}, publisher = {Zenodo}, title = {{Bidirectional electro-optic wavelength conversion in the quantum ground state}}, doi = {10.5281/ZENODO.4266025}, year = {2020}, } @article{9195, abstract = {Quantum information technology based on solid state qubits has created much interest in converting quantum states from the microwave to the optical domain. Optical photons, unlike microwave photons, can be transmitted by fiber, making them suitable for long distance quantum communication. Moreover, the optical domain offers access to a large set of very well‐developed quantum optical tools, such as highly efficient single‐photon detectors and long‐lived quantum memories. For a high fidelity microwave to optical transducer, efficient conversion at single photon level and low added noise is needed. Currently, the most promising approaches to build such systems are based on second‐order nonlinear phenomena such as optomechanical and electro‐optic interactions. Alternative approaches, although not yet as efficient, include magneto‐optical coupling and schemes based on isolated quantum systems like atoms, ions, or quantum dots. Herein, the necessary theoretical foundations for the most important microwave‐to‐optical conversion experiments are provided, their implementations are described, and the current limitations and future prospects are discussed.}, author = {Lambert, Nicholas J. and Rueda Sanchez, Alfredo R and Sedlmeir, Florian and Schwefel, Harald G. L.}, issn = {2511-9044}, journal = {Advanced Quantum Technologies}, number = {1}, publisher = {Wiley}, title = {{Coherent conversion between microwave and optical photons - An overview of physical implementations}}, doi = {10.1002/qute.201900077}, volume = {3}, year = {2020}, } @article{8755, abstract = {The superconducting circuit community has recently discovered the promising potential of superinductors. These circuit elements have a characteristic impedance exceeding the resistance quantum RQ ≈ 6.45 kΩ which leads to a suppression of ground state charge fluctuations. Applications include the realization of hardware protected qubits for fault tolerant quantum computing, improved coupling to small dipole moment objects and defining a new quantum metrology standard for the ampere. In this work we refute the widespread notion that superinductors can only be implemented based on kinetic inductance, i.e. using disordered superconductors or Josephson junction arrays. We present modeling, fabrication and characterization of 104 planar aluminum coil resonators with a characteristic impedance up to 30.9 kΩ at 5.6 GHz and a capacitance down to ≤ 1 fF, with lowloss and a power handling reaching 108 intra-cavity photons. Geometric superinductors are free of uncontrolled tunneling events and offer high reproducibility, linearity and the ability to couple magnetically - properties that significantly broaden the scope of future quantum circuits. }, author = {Peruzzo, Matilda and Trioni, Andrea and Hassani, Farid and Zemlicka, Martin and Fink, Johannes M}, issn = {23317019}, journal = {Physical Review Applied}, number = {4}, publisher = {American Physical Society}, title = {{Surpassing the resistance quantum with a geometric superinductor}}, doi = {10.1103/PhysRevApplied.14.044055}, volume = {14}, year = {2020}, } @inproceedings{10328, abstract = {We discus noise channels in coherent electro-optic up-conversion between microwave and optical fields, in particular due to optical heating. We also report on a novel configuration, which promises to be flexible and highly efficient.}, author = {Lambert, Nicholas J. and Mobassem, Sonia and Rueda Sanchez, Alfredo R and Schwefel, Harald G.L.}, booktitle = {OSA Quantum 2.0 Conference}, isbn = {9-781-5575-2820-9}, location = {Washington, DC, United States}, publisher = {Optica Publishing Group}, title = {{New designs and noise channels in electro-optic microwave to optical up-conversion}}, doi = {10.1364/QUANTUM.2020.QTu8A.1}, year = {2020}, } @inproceedings{15059, abstract = {In this paper we present a room temperature radiometer that can eliminate the need of using cryostats in satellite payload reducing its weight and improving reliability. The proposed radiometer is based on an electro-optic upconverter that boosts up microwave photons energy by upconverting them into an optical domain what makes them immune to thermal noise even if operating at room temperature. The converter uses a high-quality factor whispering gallery mode (WGM) resonator providing naturally narrow bandwidth and therefore might be useful for applications like microwave hyperspectral sensing. The upconversion process is explained by providing essential information about photon conversion efficiency and sensitivity. To prove the concept, we describe an experiment which shows state-of-the-art photon conversion efficiency n=10-5 per mW of pump power at the frequency of 80 GHz.}, author = {Wasiak, Michal and Botello, Gabriel Santamaria and Abdalmalak, Kerlos Atia and Sedlmeir, Florian and Rueda Sanchez, Alfredo R and Segovia-Vargas, Daniel and Schwefel, Harald G. L. and Munoz, Luis Enrique Garcia}, booktitle = {14th European Conference on Antennas and Propagation}, location = {Copenhagen, Denmark}, publisher = {IEEE}, title = {{Compact millimeter and submillimeter-wave photonic radiometer for cubesats}}, doi = {10.23919/eucap48036.2020.9135962}, year = {2020}, } @article{6053, abstract = {Recent technical developments in the fields of quantum electromechanics and optomechanics have spawned nanoscale mechanical transducers with the sensitivity to measure mechanical displacements at the femtometre scale and the ability to convert electromagnetic signals at the single photon level. A key challenge in this field is obtaining strong coupling between motion and electromagnetic fields without adding additional decoherence. Here we present an electromechanical transducer that integrates a high-frequency (0.42 GHz) hypersonic phononic crystal with a superconducting microwave circuit. The use of a phononic bandgap crystal enables quantum-level transduction of hypersonic mechanical motion and concurrently eliminates decoherence caused by acoustic radiation. Devices with hypersonic mechanical frequencies provide a natural pathway for integration with Josephson junction quantum circuits, a leading quantum computing technology, and nanophotonic systems capable of optical networking and distributing quantum information.}, author = {Kalaee, Mahmoud and Mirhosseini, Mohammad and Dieterle, Paul B. and Peruzzo, Matilda and Fink, Johannes M and Painter, Oskar}, issn = {1748-3395}, journal = {Nature Nanotechnology}, number = {4}, pages = {334–339}, publisher = {Springer Nature}, title = {{Quantum electromechanics of a hypersonic crystal}}, doi = {10.1038/s41565-019-0377-2}, volume = {14}, year = {2019}, } @article{6102, abstract = {Light is a union of electric and magnetic fields, and nowhere is the complex relationship between these fields more evident than in the near fields of nanophotonic structures. There, complicated electric and magnetic fields varying over subwavelength scales are generally present, which results in photonic phenomena such as extraordinary optical momentum, superchiral fields, and a complex spatial evolution of optical singularities. An understanding of such phenomena requires nanoscale measurements of the complete optical field vector. Although the sensitivity of near- field scanning optical microscopy to the complete electromagnetic field was recently demonstrated, a separation of different components required a priori knowledge of the sample. Here, we introduce a robust algorithm that can disentangle all six electric and magnetic field components from a single near-field measurement without any numerical modeling of the structure. As examples, we unravel the fields of two prototypical nanophotonic structures: a photonic crystal waveguide and a plasmonic nanowire. These results pave the way for new studies of complex photonic phenomena at the nanoscale and for the design of structures that optimize their optical behavior.}, author = {Le Feber, B. and Sipe, J. E. and Wulf, Matthias and Kuipers, L. and Rotenberg, N.}, issn = {20477538}, journal = {Light: Science and Applications}, number = {1}, publisher = {Springer Nature}, title = {{A full vectorial mapping of nanophotonic light fields}}, doi = {10.1038/s41377-019-0124-3}, volume = {8}, year = {2019}, } @article{6348, abstract = {High-speed optical telecommunication is enabled by wavelength-division multiplexing, whereby hundreds of individually stabilized lasers encode information within a single-mode optical fibre. Higher bandwidths require higher total optical power, but the power sent into the fibre is limited by optical nonlinearities within the fibre, and energy consumption by the light sources starts to become a substantial cost factor1. Optical frequency combs have been suggested to remedy this problem by generating numerous discrete, equidistant laser lines within a monolithic device; however, at present their stability and coherence allow them to operate only within small parameter ranges2,3,4. Here we show that a broadband frequency comb realized through the electro-optic effect within a high-quality whispering-gallery-mode resonator can operate at low microwave and optical powers. Unlike the usual third-order Kerr nonlinear optical frequency combs, our combs rely on the second-order nonlinear effect, which is much more efficient. Our result uses a fixed microwave signal that is mixed with an optical-pump signal to generate a coherent frequency comb with a precisely determined carrier separation. The resonant enhancement enables us to work with microwave powers that are three orders of magnitude lower than those in commercially available devices. We emphasize the practical relevance of our results to high rates of data communication. To circumvent the limitations imposed by nonlinear effects in optical communication fibres, one has to solve two problems: to provide a compact and fully integrated, yet high-quality and coherent, frequency comb generator; and to calculate nonlinear signal propagation in real time5. We report a solution to the first problem.}, author = {Rueda Sanchez, Alfredo R and Sedlmeir, Florian and Kumari, Madhuri and Leuchs, Gerd and Schwefel, Harald G.L.}, issn = {14764687}, journal = {Nature}, number = {7752}, pages = {378--381}, publisher = {Springer Nature}, title = {{Resonant electro-optic frequency comb}}, doi = {10.1038/s41586-019-1110-x}, volume = {568}, year = {2019}, } @article{6609, abstract = {Mechanical systems facilitate the development of a hybrid quantum technology comprising electrical, optical, atomic and acoustic degrees of freedom1, and entanglement is essential to realize quantum-enabled devices. Continuous-variable entangled fields—known as Einstein–Podolsky–Rosen (EPR) states—are spatially separated two-mode squeezed states that can be used for quantum teleportation and quantum communication2. In the optical domain, EPR states are typically generated using nondegenerate optical amplifiers3, and at microwave frequencies Josephson circuits can serve as a nonlinear medium4,5,6. An outstanding goal is to deterministically generate and distribute entangled states with a mechanical oscillator, which requires a carefully arranged balance between excitation, cooling and dissipation in an ultralow noise environment. Here we observe stationary emission of path-entangled microwave radiation from a parametrically driven 30-micrometre-long silicon nanostring oscillator, squeezing the joint field operators of two thermal modes by 3.40 decibels below the vacuum level. The motion of this micromechanical system correlates up to 50 photons per second per hertz, giving rise to a quantum discord that is robust with respect to microwave noise7. Such generalized quantum correlations of separable states are important for quantum-enhanced detection8 and provide direct evidence of the non-classical nature of the mechanical oscillator without directly measuring its state9. This noninvasive measurement scheme allows to infer information about otherwise inaccessible objects, with potential implications for sensing, open-system dynamics and fundamental tests of quantum gravity. In the future, similar on-chip devices could be used to entangle subsystems on very different energy scales, such as microwave and optical photons.}, author = {Barzanjeh, Shabir and Redchenko, Elena and Peruzzo, Matilda and Wulf, Matthias and Lewis, Dylan and Arnold, Georg M and Fink, Johannes M}, journal = {Nature}, pages = {480--483}, publisher = {Nature Publishing Group}, title = {{Stationary entangled radiation from micromechanical motion}}, doi = {10.1038/s41586-019-1320-2}, volume = {570}, year = {2019}, } @inproceedings{7032, abstract = {Optical frequency combs (OFCs) are light sources whose spectra consists of equally spaced frequency lines in the optical domain [1]. They have great potential for improving high-capacity data transfer, all-optical atomic clocks, spectroscopy, and high-precision measurements [2].}, author = {Rueda Sanchez, Alfredo R and Sedlmeir, Florian and Leuchs, Gerd and Kuamri, Madhuri and Schwefel, Harald G. L.}, booktitle = {2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference}, isbn = {9781728104690}, location = {Munich, Germany}, publisher = {IEEE}, title = {{Electro-optic frequency comb generation in lithium niobate whispering gallery mode resonators}}, doi = {10.1109/cleoe-eqec.2019.8873300}, year = {2019}, } @article{7156, abstract = {We propose an efficient microwave-photonic modulator as a resource for stationary entangled microwave-optical fields and develop the theory for deterministic entanglement generation and quantum state transfer in multi-resonant electro-optic systems. The device is based on a single crystal whispering gallery mode resonator integrated into a 3D-microwave cavity. The specific design relies on a new combination of thin-film technology and conventional machining that is optimized for the lowest dissipation rates in the microwave, optical, and mechanical domains. We extract important device properties from finite-element simulations and predict continuous variable entanglement generation rates on the order of a Mebit/s for optical pump powers of only a few tens of microwatts. We compare the quantum state transfer fidelities of coherent, squeezed, and non-Gaussian cat states for both teleportation and direct conversion protocols under realistic conditions. Combining the unique capabilities of circuit quantum electrodynamics with the resilience of fiber optic communication could facilitate long-distance solid-state qubit networks, new methods for quantum signal synthesis, quantum key distribution, and quantum enhanced detection, as well as more power-efficient classical sensing and modulation.}, author = {Rueda Sanchez, Alfredo R and Hease, William J and Barzanjeh, Shabir and Fink, Johannes M}, issn = {2056-6387}, journal = {npj Quantum Information}, publisher = {Springer Nature}, title = {{Electro-optic entanglement source for microwave to telecom quantum state transfer}}, doi = {10.1038/s41534-019-0220-5}, volume = {5}, year = {2019}, } @article{7451, abstract = {We prove that the observable telegraph signal accompanying the bistability in the photon-blockade-breakdown regime of the driven and lossy Jaynes–Cummings model is the finite-size precursor of what in the thermodynamic limit is a genuine first-order phase transition. We construct a finite-size scaling of the system parameters to a well-defined thermodynamic limit, in which the system remains the same microscopic system, but the telegraph signal becomes macroscopic both in its timescale and intensity. The existence of such a finite-size scaling completes and justifies the classification of the photon-blockade-breakdown effect as a first-order dissipative quantum phase transition.}, author = {Vukics, A. and Dombi, A. and Fink, Johannes M and Domokos, P.}, issn = {2521-327X}, journal = {Quantum}, publisher = {Verein zur Förderung des Open Access Publizierens in den Quantenwissenschaften}, title = {{Finite-size scaling of the photon-blockade breakdown dissipative quantum phase transition}}, doi = {10.22331/q-2019-06-03-150}, volume = {3}, year = {2019}, } @inproceedings{7233, abstract = {We demonstrate electro-optic frequency comb generation using a doubly resonant system comprising a whispering gallery mode disk resonator made of lithium niobate mounted inside a three dimensional copper cavity. We observe 180 sidebands centred at 1550 nm.}, author = {Rueda Sanchez, Alfredo R and Sedlmeir, Florian and Leuchs, Gerd and Kumari, Madhuri and Schwefel, Harald G.L.}, booktitle = {Nonlinear Optics, OSA Technical Digest}, isbn = {9781557528209}, location = {Waikoloa Beach, Hawaii (HI), United States}, publisher = {Optica Publishing Group}, title = {{Resonant electro-optic frequency comb generation in lithium niobate disk resonator inside a microwave cavity}}, doi = {10.1364/NLO.2019.NM2A.5}, year = {2019}, } @article{287, abstract = {In this paper, we discuss biological effects of electromagnetic (EM) fields in the context of cancer biology. In particular, we review the nanomechanical properties of microtubules (MTs), the latter being one of the most successful targets for cancer therapy. We propose an investigation on the coupling of electromagnetic radiation to mechanical vibrations of MTs as an important basis for biological and medical applications. In our opinion, optomechanical methods can accurately monitor and control the mechanical properties of isolated MTs in a liquid environment. Consequently, studying nanomechanical properties of MTs may give useful information for future applications to diagnostic and therapeutic technologies involving non-invasive externally applied physical fields. For example, electromagnetic fields or high intensity ultrasound can be used therapeutically avoiding harmful side effects of chemotherapeutic agents or classical radiation therapy.}, author = {Salari, Vahid and Barzanjeh, Shabir and Cifra, Michal and Simon, Christoph and Scholkmann, Felix and Alirezaei, Zahra and Tuszynski, Jack}, journal = {Frontiers in Bioscience - Landmark}, number = {8}, pages = {1391 -- 1406}, publisher = {Frontiers in Bioscience}, title = {{Electromagnetic fields and optomechanics In cancer diagnostics and treatment}}, doi = {10.2741/4651}, volume = {23}, year = {2018}, } @article{436, abstract = {There has been significant interest recently in using complex quantum systems to create effective nonreciprocal dynamics. Proposals have been put forward for the realization of artificial magnetic fields for photons and phonons; experimental progress is fast making these proposals a reality. Much work has concentrated on the use of such systems for controlling the flow of signals, e.g., to create isolators or directional amplifiers for optical signals. In this Letter, we build on this work but move in a different direction. We develop the theory of and discuss a potential realization for the controllable flow of thermal noise in quantum systems. We demonstrate theoretically that the unidirectional flow of thermal noise is possible within quantum cascaded systems. Viewing an optomechanical platform as a cascaded system we show here that one can ultimately control the direction of the flow of thermal noise. By appropriately engineering the mechanical resonator, which acts as an artificial reservoir, the flow of thermal noise can be constrained to a desired direction, yielding a thermal rectifier. The proposed quantum thermal noise rectifier could potentially be used to develop devices such as a thermal modulator, a thermal router, and a thermal amplifier for nanoelectronic devices and superconducting circuits.}, author = {Barzanjeh, Shabir and Aquilina, Matteo and Xuereb, André}, journal = {Physical Review Letters}, number = {6}, publisher = {American Physical Society}, title = {{Manipulating the flow of thermal noise in quantum devices}}, doi = {10.1103/PhysRevLett.120.060601}, volume = {120}, year = {2018}, } @article{307, abstract = {Spontaneous emission spectra of two initially excited closely spaced identical atoms are very sensitive to the strength and the direction of the applied magnetic field. We consider the relevant schemes that ensure the determination of the mutual spatial orientation of the atoms and the distance between them by entirely optical means. A corresponding theoretical description is given accounting for the dipole-dipole interaction between the two atoms in the presence of a magnetic field and for polarizations of the quantum field interacting with magnetic sublevels of the two-atom system. }, author = {Redchenko, Elena and Makarov, Alexander and Yudson, Vladimir}, journal = { Physical Review A - Atomic, Molecular, and Optical Physics}, number = {4}, publisher = {American Physical Society}, title = {{Nanoscopy of pairs of atoms by fluorescence in a magnetic field}}, doi = {10.1103/PhysRevA.97.043812}, volume = {97}, year = {2018}, } @inproceedings{155, abstract = {There is currently significant interest in operating devices in the quantum regime, where their behaviour cannot be explained through classical mechanics. Quantum states, including entangled states, are fragile and easily disturbed by excessive thermal noise. Here we address the question of whether it is possible to create non-reciprocal devices that encourage the flow of thermal noise towards or away from a particular quantum device in a network. Our work makes use of the cascaded systems formalism to answer this question in the affirmative, showing how a three-port device can be used as an effective thermal transistor, and illustrates how this formalism maps onto an experimentally-realisable optomechanical system. Our results pave the way to more resilient quantum devices and to the use of thermal noise as a resource.}, author = {Xuereb, André and Aquilina, Matteo and Barzanjeh, Shabir}, editor = {Andrews, D L and Ostendorf, A and Bain, A J and Nunzi, J M}, location = {Strasbourg, France}, publisher = {SPIE}, title = {{Routing thermal noise through quantum networks}}, doi = {10.1117/12.2309928}, volume = {10672}, year = {2018}, } @article{22, abstract = {Conventional ultra-high sensitivity detectors in the millimeter-wave range are usually cooled as their own thermal noise at room temperature would mask the weak received radiation. The need for cryogenic systems increases the cost and complexity of the instruments, hindering the development of, among others, airborne and space applications. In this work, the nonlinear parametric upconversion of millimeter-wave radiation to the optical domain inside high-quality (Q) lithium niobate whispering-gallery mode (WGM) resonators is proposed for ultra-low noise detection. We experimentally demonstrate coherent upconversion of millimeter-wave signals to a 1550 nm telecom carrier, with a photon conversion efficiency surpassing the state-of-the-art by 2 orders of magnitude. Moreover, a theoretical model shows that the thermal equilibrium of counterpropagating WGMs is broken by overcoupling the millimeter-wave WGM, effectively cooling the upconverted mode and allowing ultra-low noise detection. By theoretically estimating the sensitivity of a correlation radiometer based on the presented scheme, it is found that room-temperature radiometers with better sensitivity than state-of-the-art high-electron-mobility transistor (HEMT)-based radiometers can be designed. This detection paradigm can be used to develop room-temperature instrumentation for radio astronomy, earth observation, planetary missions, and imaging systems.}, author = {Botello, Gabriel and Sedlmeir, Florian and Rueda Sanchez, Alfredo R and Abdalmalak, Kerlos and Brown, Elliott and Leuchs, Gerd and Preu, Sascha and Segovia Vargas, Daniel and Strekalov, Dmitry and Munoz, Luis and Schwefel, Harald}, issn = {23342536}, journal = {Optica}, number = {10}, pages = {1210 -- 1219}, title = {{Sensitivity limits of millimeter-wave photonic radiometers based on efficient electro-optic upconverters}}, doi = {10.1364/OPTICA.5.001210}, volume = {5}, year = {2018}, } @article{1013, abstract = {From microwave ovens to satellite television to the GPS and data services on our mobile phones, microwave technology is everywhere today. But one technology that has so far failed to prove its worth in this wavelength regime is quantum communication that uses the states of single photons as information carriers. This is because single microwave photons, as opposed to classical microwave signals, are extremely vulnerable to noise from thermal excitations in the channels through which they travel. Two new independent studies, one by Ze-Liang Xiang at Technische Universität Wien (Vienna), Austria, and colleagues [1] and another by Benoît Vermersch at the University of Innsbruck, also in Austria, and colleagues [2] now describe a theoretical protocol for microwave quantum communication that is resilient to thermal and other types of noise. Their approach could become a powerful technique to establish fast links between superconducting data processors in a future all-microwave quantum network.}, author = {Fink, Johannes M}, journal = {Physics}, number = {32}, publisher = {American Physical Society}, title = {{Viewpoint: Microwave quantum states beat the heat}}, doi = {10.1103/Physics.10.32}, volume = {10}, year = {2017}, } @article{700, abstract = {Microtubules provide the mechanical force required for chromosome separation during mitosis. However, little is known about the dynamic (high-frequency) mechanical properties of microtubules. Here, we theoretically propose to control the vibrations of a doubly clamped microtubule by tip electrodes and to detect its motion via the optomechanical coupling between the vibrational modes of the microtubule and an optical cavity. In the presence of a red-detuned strong pump laser, this coupling leads to optomechanical-induced transparency of an optical probe field, which can be detected with state-of-the art technology. The center frequency and line width of the transparency peak give the resonance frequency and damping rate of the microtubule, respectively, while the height of the peak reveals information about the microtubule-cavity field coupling. Our method opens the new possibilities to gain information about the physical properties of microtubules, which will enhance our capability to design physical cancer treatment protocols as alternatives to chemotherapeutic drugs.}, author = {Barzanjeh, Shabir and Salari, Vahid and Tuszynski, Jack and Cifra, Michal and Simon, Christoph}, issn = {24700045}, journal = { Physical Review E Statistical Nonlinear and Soft Matter Physics }, number = {1}, publisher = {American Institute of Physics}, title = {{Optomechanical proposal for monitoring microtubule mechanical vibrations}}, doi = {10.1103/PhysRevE.96.012404}, volume = {96}, year = {2017}, } @article{797, abstract = {Phasenübergänge helfen beim Verständnis von Vielteilchensystemen in der Festkörperphysik und Fluiddynamik bis hin zur Teilchenphysik. Unserer internationalen Kollaboration ist es gelungen, einen neuartigen Phasenübergang in einem Quantensystem zu beobachten [1]. In einem Mikrowellenresonator konnte erstmals die spontane Zustandsänderung von undurchsichtig zu transparent nachgewiesen werden.}, author = {Fink, Johannes M}, journal = {Physik in unserer Zeit}, number = {3}, pages = {111 -- 113}, publisher = {Wiley}, title = {{Photonenblockade aufgelöst}}, doi = {10.1002/piuz.201770305}, volume = {48}, year = {2017}, }