TY - GEN
AB - Mitchison and Jozsa recently suggested that the "chained-Zeno" counterfactual computation protocol recently proposed by Hosten et al. is counterfactual for only one output of the computer. This claim was based on the existing abstract algebraic definition of counterfactual computation, and indeed according to this definition, their argument is correct. However, a more general definition (physically adequate) for counterfactual computation is implicitly assumed by Hosten et. al. Here we explain in detail why the protocol is counterfactual and how the "history tracking" method of the existing description inadequately represents the physics underlying the protocol. Consequently, we propose a modified definition of counterfactual computation. Finally, we comment on one of the most interesting aspects of the error-correcting protocol.
AU - Hosten, Onur
AU - Rakher, Matthew
AU - Barreiro, Julio
AU - Peters, Nicholas
AU - Kwiat, Paul
ID - 573
TI - Counterfactual computation revisited
ER -
TY - GEN
AB - Vaidman, in a recent article adopts the method of 'quantum weak measurements in pre- and postselected ensembles' to ascertain whether or not the chained-Zeno counterfactual computation scheme proposed by Hosten et al. is counterfactual; which has been the topic of a debate on the definition of counterfactuality. We disagree with his conclusion, which brings up some interesting aspects of quantum weak measurements and some concerns about the way they are interpreted.
AU - Hosten, Onur
AU - Kwiat, Paul
ID - 574
TI - Weak measurements and counterfactual computation
ER -
TY - CONF
AB - Visible light photon counters (VLPCs) and solid-state photomultipliers (SSPMs) are high-efficiency single-photon detectors which have multi-photon counting capability. While both the VLPCs and the SSPMs have inferred internal quantum efficiencies above 93%, the actual measured values for both the detectors were in fact limited to less than 88%, attributed to in-coupling losses. We are currently improving this overall detection efficiency via a) custom anti-reflection coating the detectors and the in-coupling fibers, b) implementing a novel cryogenic design to reduce transmission losses and, c) using low-noise electronics to obtain a better signal-to-noise ratio.
AU - Rangarajan, Radhika
AU - Altepeter, Joseph B
AU - Jeffrey, Evan R
AU - Stoutimore, Micah J
AU - Peters, Nicholas A
AU - Onur Hosten
AU - Kwiat, Paul G
ID - 577
TI - High-efficiency single-photon detectors
VL - 6372
ER -
TY - CONF
AB - A source of single photons allows secure quantum key distribution, in addition, to being a critical resource for linear optics quantum computing. We describe our progress on deterministically creating single photons from spontaneous parametric downconversion, an extension of the Pittman, Jacobs and Franson scheme [Phys. Rev A, v66, 042303 (2002)]. Their idea was to conditionally prepare single photons by measuring one member of a spontaneously emitted photon pair and storing the remaining conditionally prepared photon until a predetermined time, when it would be "deterministically" released from storage. Our approach attempts to improve upon this by recycling the pump pulse in order to decrease the possibility of multiple-pair generation, while maintaining a high probability of producing a single pair. Many of the challenges we discuss are central to other quantum information technologies, including the need for low-loss optical storage, switching and detection, and fast feed-forward control.
AU - Peters, Nicholas A
AU - Arnold, Keith J
AU - VanDevender, Aaron P
AU - Jeffrey, Evan R
AU - Rangarajan, Radhika
AU - Onur Hosten
AU - Barreiro, Julio T
AU - Altepeter, Joseph B
AU - Kwiat, Paul G
ID - 578
TI - Towards a quasi-deterministic single-photon source
VL - 6305
ER -
TY - JOUR
AB - The logic underlying the coherent nature of quantum information processing often deviates from intuitive reasoning, leading to surprising effects. Counterfactual computation constitutes a striking example: the potential outcome of a quantum computation can be inferred, even if the computer is not run 1. Relying on similar arguments to interaction-free measurements 2 (or quantum interrogation3), counterfactual computation is accomplished by putting the computer in a superposition of 'running' and 'not running' states, and then interfering the two histories. Conditional on the as-yet-unknown outcome of the computation, it is sometimes possible to counterfactually infer information about the solution. Here we demonstrate counterfactual computation, implementing Grover's search algorithm with an all-optical approach4. It was believed that the overall probability of such counterfactual inference is intrinsically limited1,5, so that it could not perform better on average than random guesses. However, using a novel 'chained' version of the quantum Zeno effect6, we show how to boost the counterfactual inference probability to unity, thereby beating the random guessing limit. Our methods are general and apply to any physical system, as illustrated by a discussion of trapped-ion systems. Finally, we briefly show that, in certain circumstances, counterfactual computation can eliminate errors induced by decoherence.
AU - Onur Hosten
AU - Rakher, Matthew T
AU - Barreiro, Julio T
AU - Peters, Nicholas A
AU - Kwiat, Paul G
ID - 579
IS - 7079
JF - Nature
TI - Counterfactual quantum computation through quantum interrogation
VL - 439
ER -
TY - CONF
AB - Visible light photon counters (VLPCs) and solid-state photomultipliers (SSPMs) facilitate efficient single-photon detection. We are attempting to improve their efficiency, previously limited to < 88% by coupling losses, via anti-reflection coatings, better electronics and cryogenics.
AU - Rangarajan, Radhika
AU - Peters, Nicholas A
AU - Onur Hosten
AU - Altepeter, Joseph B
AU - Jeffrey, Evan R
AU - Kwiat, Paul G
ID - 583
TI - Improved single-photon detection
ER -
TY - JOUR
AU - Salecker, Iris
AU - Häusser, Michael
AU - de Bono, Mario
ID - 6151
IS - 6
JF - EMBO reports
SN - 1469-221X
TI - On the axonal road to circuit function and behaviour: Workshop on the assembly and function of neuronal circuits
VL - 7
ER -
TY - JOUR
AU - Rogers, Candida
AU - Persson, Annelie
AU - Cheung, Benny
AU - de Bono, Mario
ID - 6152
IS - 7
JF - Current Biology
SN - 0960-9822
TI - Behavioral motifs and neural pathways coordinating O2 responses and aggregation in C. elegans
VL - 16
ER -
TY - JOUR
AB - This note proves combinatorially that the intersection pairing on the middle-dimensional compactly supported cohomology of a toric hyperkähler variety is always definite, providing a large number of non-trivial L 2 harmonic forms for toric hyperkähler metrics on these varieties. This is motivated by a result of Hitchin about the definiteness of the pairing of L 2 harmonic forms on complete hyperkähler manifolds of linear growth.
AU - Tamas Hausel
AU - Swartz, Edward
ID - 1461
IS - 8
JF - Proceedings of the American Mathematical Society
TI - Intersection forms of toric hyperkähler varieties
VL - 134
ER -
TY - JOUR
AB - A Fourier transform technique is introduced for counting the number of solutions of holomorphic moment map equations over a finite field. This technique in turn gives information on Betti numbers of holomorphic symplectic quotients. As a consequence, simple unified proofs are obtained for formulas of Poincaré polynomials of toric hyperkähler varieties (recovering results of Bielawski-Dancer and Hausel-Sturmfels), Poincaré polynomials of Hubert schemes of points and twisted Atiyah-Drinfeld-Hitchin-Manin (ADHM) spaces of instantons on ℂ2 (recovering results of Nakajima-Yoshioka), and Poincaré polynomials of all Nakajima quiver varieties. As an application, a proof of a conjecture of Kac on the number of absolutely indecomposable representations of a quiver is announced.
AU - Tamas Hausel
ID - 1462
IS - 16
JF - PNAS
TI - Betti numbers of holomorphic symplectic quotients via arithmetic Fourier transform
VL - 103
ER -