@article{14802, abstract = {Frequency-stable lasers form the back bone of precision measurements in science and technology. Such lasers typically attain their stability through frequency locking to reference cavities. State-of-the-art locking performances to date had been achieved using frequency modulation based methods, complemented with active drift cancellation systems. We demonstrate an all passive, modulation-free laser-cavity locking technique (squash locking) that utilizes changes in spatial beam ellipticity for error signal generation, and a coherent polarization post-selection for noise resilience. By comparing two identically built proof-of-principle systems, we show a frequency locking instability of 5×10−7 relative to the cavity linewidth at 10 s averaging. The results surpass the demonstrated performances of methods engineered over the last five decades, potentially enabling an advancement in the precision control of lasers, while creating avenues for bridging the performance gaps between industrial grade lasers with scientific ones due to the afforded simplicity and scalability.}, author = {Diorico, Fritz R and Zhutov, Artem and Hosten, Onur}, issn = {2334-2536}, journal = {Optica}, keywords = {Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials}, number = {1}, pages = {26--31}, publisher = {Optica Publishing Group}, title = {{Laser-cavity locking utilizing beam ellipticity: accessing the 10−7 instability scale relative to cavity linewidth}}, doi = {10.1364/optica.507451}, volume = {11}, year = {2024}, } @article{14980, abstract = {Precision sensing and manipulation of milligram-scale mechanical oscillators has attracted growing interest in the fields of table-top explorations of gravity and tests of quantum mechanics at macroscopic scales. Torsional oscillators present an opportunity in this regard due to their remarked isolation from environmental noise. For torsional motion, an effective employment of optical cavities to enhance optomechanical interactions—as already established for linear oscillators—so far faced certain challenges. Here, we propose a concept for sensing and manipulating torsional motion, where exclusively the torsional rotations of a pendulum are mapped onto the path length of a single two-mirror optical cavity. The concept inherently alleviates many limitations of previous approaches. A proof-of-principle experiment is conducted with a rigidly controlled pendulum to explore the sensing aspects of the concept and to identify practical limitations in a potential state-of-the art setup. Based on this study, we anticipate development of precision torque sensors utilizing torsional pendulums that can support sensitivities below 10−19Nm/√Hz, while the motion of the pendulums are dominated by quantum radiation pressure noise at sub-microwatts of incoming laser power. These developments will provide horizons for experiments at the interface of quantum mechanics and gravity.}, author = {Agafonova, Sofya and Mishra, Umang and Diorico, Fritz R and Hosten, Onur}, issn = {2643-1564}, journal = {Physical Review Research}, number = {1}, publisher = {American Physical Society}, title = {{Zigzag optical cavity for sensing and controlling torsional motion}}, doi = {10.1103/physrevresearch.6.013141}, volume = {6}, year = {2024}, } @article{14749, abstract = {We unveil a powerful method for the stabilization of laser injection locking based on sensing variations in the output beam ellipticity of an optically seeded laser. The effect arises due to an interference between the seeding beam and the injected laser output. We demonstrate the method for a commercial semiconductor laser without the need for any internal changes to the readily operational injection locked laser system that was used. The method can also be used to increase the mode-hop free tuning range of lasers, and has the potential to fill a void in the low-noise laser industry.}, author = {Mishra, Umang and Li, Vyacheslav and Wald, Sebastian and Agafonova, Sofya and Diorico, Fritz R and Hosten, Onur}, issn = {1539-4794}, journal = {Optics Letters}, keywords = {Atomic and Molecular Physics, and Optics}, number = {15}, pages = {3973--3976}, publisher = {Optica Publishing Group}, title = {{Monitoring and active stabilization of laser injection locking using beam ellipticity}}, doi = {10.1364/ol.495553}, volume = {48}, year = {2023}, } @article{14759, abstract = {Proper operation of electro-optic I/Q modulators relies on precise adjustment and control of the relative phase biases between the modulator’s internal interferometer arms. We present an all-analog phase bias locking scheme where error signals are obtained from the beat between the optical carrier and optical tones generated by an auxiliary 2 MHz 𝑅𝐹 tone to lock the phases of all three involved interferometers for operation up to 10 GHz. With the developed method, we demonstrate an I/Q modulator in carrier-suppressed single-sideband mode, where the suppressed carrier and sideband are locked at optical power levels <−27dB relative to the transmitted sideband. We describe a simple analytical model for calculating the error signals and detail the implementation of the electronic circuitry for the implementation of the method.}, author = {Wald, Sebastian and Diorico, Fritz R and Hosten, Onur}, issn = {2155-3165}, journal = {Applied Optics}, keywords = {Atomic and Molecular Physics, and Optics, Engineering (miscellaneous), Electrical and Electronic Engineering}, number = {1}, pages = {1--7}, publisher = {Optica Publishing Group}, title = {{Analog stabilization of an electro-optic I/Q modulator with an auxiliary modulation tone}}, doi = {10.1364/ao.474118}, volume = {62}, year = {2023}, } @article{10652, abstract = {Finding a feasible scheme for testing the quantum mechanical nature of the gravitational interaction has been attracting an increasing level of attention. Gravity mediated entanglement generation so far appears to be the key ingredient for a potential experiment. In a recent proposal [D. Carney et al., PRX Quantum 2, 030330 (2021)] combining an atom interferometer with a low-frequency mechanical oscillator, a coherence revival test is proposed for verifying this entanglement generation. With measurements performed only on the atoms, this protocol bypasses the need for correlation measurements. Here, we explore formulations of such a protocol, and specifically find that in the envisioned regime of operation with high thermal excitation, semiclassical models, where there is no concept of entanglement, also give the same experimental signatures. We elucidate in a fully quantum mechanical calculation that entanglement is not the source of the revivals in the relevant parameter regime. We argue that, in its current form, the suggested test is only relevant if the oscillator is nearly in a pure quantum state, and in this regime the effects are too small to be measurable. We further discuss potential open ends. The results highlight the importance and subtleties of explicitly considering how the quantum case differs from the classical expectations when testing for the quantum mechanical nature of a physical system.}, author = {Hosten, Onur}, issn = {2643-1564}, journal = {Physical Review Research}, number = {1}, publisher = {American Physical Society}, title = {{Constraints on probing quantum coherence to infer gravitational entanglement}}, doi = {10.1103/PhysRevResearch.4.013023}, volume = {4}, year = {2022}, } @article{11438, abstract = {Lasers with well-controlled relative frequencies are indispensable for many applications in science and technology. We present a frequency-offset locking method for lasers based on beat-frequency discrimination utilizing hybrid electronic LC filters. The method is specifically designed for decoupling the tightness of the lock from the broadness of its capture range. The presented demonstration locks two free-running diode lasers at 780 nm with a 5.5-GHz offset. It displays an offset frequency instability below 55 Hz for time scales in excess of 1000 s and a minimum of 12 Hz at 10-s averaging. The performance is complemented with a 190-MHz lock-capture range, a tuning range of up to 1 GHz, and a frequency ramp agility of 200kHz/μs.}, author = {Li, Vyacheslav and Diorico, Fritz R and Hosten, Onur}, issn = {2331-7019}, journal = {Physical Review Applied}, keywords = {General Physics and Astronomy}, number = {5}, publisher = {American Physical Society}, title = {{Laser frequency-offset locking at 10-Hz-level instability using hybrid electronic filters}}, doi = {10.1103/physrevapplied.17.054031}, volume = {17}, year = {2022}, } @article{9331, abstract = {Quantum entanglement has been generated and verified in cold-atom experiments and used to make atom-interferometric measurements below the shot-noise limit. However, current state-of-the-art cold-atom devices exploit separable (i.e., unentangled) atomic states. This perspective piece asks the question: can entanglement usefully improve cold-atom sensors, in the sense that it gives new sensing capabilities unachievable with current state-of-the-art devices? We briefly review the state-of-the-art in precision cold-atom sensing, focusing on clocks and inertial sensors, identifying the potential benefits entanglement could bring to these devices, and the challenges that need to be overcome to realize these benefits. We survey demonstrated methods of generating metrologically useful entanglement in cold-atom systems, note their relative strengths and weaknesses, and assess their prospects for near-to-medium term quantum-enhanced cold-atom sensing.}, author = {Szigeti, Stuart S. and Hosten, Onur and Haine, Simon A.}, issn = {00036951}, journal = {Applied Physics Letters}, number = {14}, publisher = {AIP Publishing}, title = {{Improving cold-atom sensors with quantum entanglement: Prospects and challenges}}, doi = {10.1063/5.0050235}, volume = {118}, year = {2021}, } @article{8285, abstract = {We demonstrate the utility of optical cavity generated spin-squeezed states in free space atomic fountain clocks in ensembles of 390 000 87Rb atoms. Fluorescence imaging, correlated to an initial quantum nondemolition measurement, is used for population spectroscopy after the atoms are released from a confining lattice. For a free fall time of 4 milliseconds, we resolve a single-shot phase sensitivity of 814(61) microradians, which is 5.8(0.6) decibels (dB) below the quantum projection limit. We observe that this squeezing is preserved as the cloud expands to a roughly 200  μm radius and falls roughly 300  μm in free space. Ramsey spectroscopy with 240 000 atoms at a 3.6 ms Ramsey time results in a single-shot fractional frequency stability of 8.4(0.2)×10−12, 3.8(0.2) dB below the quantum projection limit. The sensitivity and stability are limited by the technical noise in the fluorescence detection protocol and the microwave system, respectively.}, author = {Malia, Benjamin K. and Martínez-Rincón, Julián and Wu, Yunfan and Hosten, Onur and Kasevich, Mark A.}, issn = {1079-7114}, journal = {Physical Review Letters}, number = {4}, publisher = {American Physical Society}, title = {{Free space Ramsey spectroscopy in rubidium with noise below the quantum projection limit}}, doi = {10.1103/PhysRevLett.125.043202}, volume = {125}, year = {2020}, } @article{8319, abstract = {We demonstrate that releasing atoms into free space from an optical lattice does not deteriorate cavity-generated spin squeezing for metrological purposes. In this work, an ensemble of 500000 spin-squeezed atoms in a high-finesse optical cavity with near-uniform atom-cavity coupling is prepared, released into free space, recaptured in the cavity, and probed. Up to ∼10 dB of metrologically relevant squeezing is retrieved for 700μs free-fall times, and decaying levels of squeezing are realized for up to 3 ms free-fall times. The degradation of squeezing results from loss of atom-cavity coupling homogeneity between the initial squeezed state generation and final collective state readout. A theoretical model is developed to quantify this degradation and this model is experimentally validated.}, author = {Wu, Yunfan and Krishnakumar, Rajiv and Martínez-Rincón, Julián and Malia, Benjamin K. and Hosten, Onur and Kasevich, Mark A.}, issn = {24699934}, journal = {Physical Review A}, number = {1}, publisher = {American Physical Society}, title = {{Retrieval of cavity-generated atomic spin squeezing after free-space release}}, doi = {10.1103/PhysRevA.102.012224}, volume = {102}, year = {2020}, } @article{593, abstract = {Bell correlations, indicating nonlocality in composite quantum systems, were until recently only seen in small systems. Here, we demonstrate Bell correlations in squeezed states of 5×105 Rb87 atoms. The correlations are inferred using collective measurements as witnesses and are statistically significant to 124 standard deviations. The states are both generated and characterized using optical-cavity aided measurements.}, author = {Engelsen, Nils and Krishnakumar, Rajiv and Hosten, Onur and Kasevich, Mark}, journal = {Physical Review Letters}, number = {14}, publisher = {American Physical Society}, title = {{Bell correlations in spin-squeezed states of 500 000 atoms}}, doi = {10.1103/PhysRevLett.118.140401}, volume = {118}, year = {2017}, } @article{588, abstract = {Quantum metrology uses quantum entanglement - correlations in the properties of microscopic systems - to improve the statistical precision of physical measurements. When measuring a signal, such as the phase shift of a light beam or an atomic state, a prominent limitation to achievable precision arises from the noise associated with the counting of uncorrelated probe particles. This noise, commonly referred to as shot noise or projection noise, gives rise to the standard quantum limit (SQL) to phase resolution. However, it can be mitigated down to the fundamental Heisenberg limit by entangling the probe particles. Despite considerable experimental progress in a variety of physical systems, a question that persists is whether these methods can achieve performance levels that compare favourably with optimized conventional (non-entangled) systems. Here we demonstrate an approach that achieves unprecedented levels of metrological improvement using half a million 87Rb atoms in their 'clock' states. The ensemble is 20.1 ± 0.3 decibels (100-fold) spin-squeezed via an optical-cavity-based measurement. We directly resolve small microwave-induced rotations 18.5 ± 0.3 decibels (70-fold) beyond the SQL. The single-shot phase resolution of 147 microradians achieved by the apparatus is better than that achieved by the best engineered cold atom sensors despite lower atom numbers. We infer entanglement of more than 680 ± 35 particles in the atomic ensemble. Applications include atomic clocks, inertial sensors, and fundamental physics experiments such as tests of general relativity or searches for electron electric dipole moment. To this end, we demonstrate an atomic clock measurement with a quantum enhancement of 10.5 ± 0.3 decibels (11-fold), limited by the phase noise of our microwave source.}, author = {Onur Hosten and Engelsen, Nils J and Krishnakumar, Rajiv and Kasevich, Mark A}, journal = {Nature}, number = {7587}, pages = {505 -- 508}, publisher = {Nature Publishing Group}, title = {{Measurement noise 100 times lower than the quantum-projection limit using entangled atoms}}, doi = {10.1038/nature16176}, volume = {529}, year = {2016}, } @article{587, abstract = {Quantum metrology exploits entangled states of particles to improve sensing precision beyond the limit achievable with uncorrelated particles. All previous methods required detection noise levels below this standard quantum limit to realize the benefits of the intrinsic sensitivity provided by these states.We experimentally demonstrate a widely applicable method for entanglement-enhanced measurements without low-noise detection. The method involves an intermediate quantum phase magnification step that eases implementation complexity. We used it to perform squeezed-state metrology 8 decibels below the standard quantum limit with a detection system that has a noise floor 10 decibels above the standard quantum limit.}, author = {Onur Hosten and Krishnakumar, Rajiv and Engelsen, Nils J and Kasevich, Mark A}, journal = {Science}, number = {6293}, pages = {1552 -- 1555}, publisher = {American Association for the Advancement of Science}, title = {{Quantum phase magnification}}, doi = {10.1126/science.aaf3397}, volume = {352}, year = {2016}, } @inproceedings{592, abstract = {We create up to 20 dB spin-squeezed states of atomic ensembles using an optical cavity-based measurement. The prepared states are suitable for atomic sensors that require free space release of the atoms.}, author = {Engelsen, Nils and Hosten, Onur and Krishnakumar, Rajiv and Kasevich, Mark}, location = {San Jose, CA, United States}, publisher = {IEEE}, title = {{Engineering spin squeezed states for quantum-enhanced atom interferometry}}, year = {2016}, } @article{589, abstract = {We demonstrate a many-atom-cavity system with a high-finesse dual-wavelength standing wave cavity in which all participating rubidium atoms are nearly identically coupled to a 780-nm cavity mode. This homogeneous coupling is enforced by a one-dimensional optical lattice formed by the field of a 1560-nm cavity mode.}, author = {Lee, Jongmin and Vrijsen, Geert and Teper, Igor and Onur Hosten and Kasevich, Mark A}, journal = {Optics Letters}, number = {13}, pages = {4005 -- 4008}, publisher = {OSA}, title = {{Many-atom-cavity QED system with homogeneous atom-cavity coupling}}, doi = {10.1364/OL.39.004005}, volume = {39}, year = {2014}, } @inproceedings{590, abstract = {We present two methods of creating two orthogonally-polarized focal points at customizable relative locations. These schemes may be critical for enhancing entanglement sources and other applications.}, author = {Schmid, David and Huang, Ting-Yu and Dirks, Radhika and Onur Hosten and Kwiat, Paul G}, publisher = {OSA}, title = {{Polarization dependent focusing}}, doi = {10.1364/QIM.2013.W6.23}, year = {2013}, } @article{591, abstract = {We present two methods for the precise independent focusing of orthogonal linear polarizations of light at arbitrary relative locations. Our first scheme uses a displaced lens in a polarization Sagnac interferometer to provide adjustable longitudinal and lateral focal displacements via simple geometry; the second uses uniaxial crystals to achieve the same effect in a compact collinear setup. We develop the theoretical applications and limitations of our schemes, and provide experimental confirmation of our calculations.}, author = {Schmid, David and Huang, Ting-Yu and Hazrat, Shiraz and Dirks, Radhika and Onur Hosten and Quint, Stephan and Thian, Dickson and Kwiat, Paul G}, journal = {Optics Express}, number = {13}, pages = {15538 -- 15552}, publisher = {Optical Society of America}, title = {{Adjustable and robust methods for polarization-dependent focusing}}, doi = {10.1364/OE.21.015538}, volume = {21}, year = {2013}, } @article{580, author = {Onur Hosten}, journal = {Nature}, number = {7350}, pages = {170 -- 171}, publisher = {Nature Publishing Group}, title = {{Quantum physics: How to catch a wave}}, doi = {10.1038/474170a}, volume = {474}, year = {2011}, } @inproceedings{585, abstract = {We present two independent schemes for the precise focusing of orthogonal polarizations of light at arbitrary relative locations. The first scheme uses a polarization Sagnac interferometer, the second a set of three birefringent elements. }, author = {Schmid, David and Hazrat, Shiraz and Rangarajan, Radhika and Onur Hosten and Quint, Stephan and Kwiat, Paul G}, publisher = {OSA}, title = {{Methods towards achieving precise birefringent focusing}}, doi = {10.1364/CLEO_AT.2011.JThB130}, year = {2011}, } @article{586, abstract = {We demonstrate a Raman laser using cold Rb87 atoms as the gain medium in a high-finesse optical cavity. We observe robust continuous wave lasing in the atypical regime where single atoms can considerably affect the cavity field. Consequently, we discover unusual lasing threshold behavior in the system causing jumps in lasing power, and propose a model to explain the effect. We also measure the intermode laser linewidth, and observe values as low as 80Hz. The tunable gain properties of this laser suggest multiple directions for future research.}, author = {Vrijsen, Geert and Onur Hosten and Lee, Jongmin and Bernon, Simon and Kasevich, Mark A}, journal = {Physical Review Letters}, number = {6}, publisher = {American Physical Society}, title = {{Raman lasing with a cold atom gain medium in a high-finesse optical cavity}}, doi = {10.1103/PhysRevLett.107.063904}, volume = {107}, year = {2011}, } @article{581, abstract = {We have detected a spin-dependent displacement perpendicular to the refractive index gradient for photons passing through an air-glass interface. The effect is the photonic version of the spin Hall effect in electronic systems, indicating the universality of the effect for particles of different nature. Treating the effect as a weak measurement of the spin projection of the photons, we used a preselection and postselection technique on the spin state to enhance the original displacement by nearly four orders of magnitude, attaining sensitivity to displacements of ∼1 angstrom. The spin Hall effect can be used for manipulating photonic angular momentum states, and the measurement technique holds promise for precision metrology.}, author = {Onur Hosten and Kwiat, Paul}, journal = {Science}, number = {5864}, pages = {787 -- 790}, publisher = {American Association for the Advancement of Science}, title = {{Observation of the spin hall effect of light via weak measurements}}, doi = {10.1126/science.1152697}, volume = {319}, year = {2008}, }