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Articles 1 - 15 of 15
Full-Text Articles in Physics
Device-Independent Quantum Key Distribution With Generalized Two-Mode Schrödinger Cat States, Curtis J. Broadbent, Kevin Marshall, Christian Weedbrook, John C. Howell
Device-Independent Quantum Key Distribution With Generalized Two-Mode Schrödinger Cat States, Curtis J. Broadbent, Kevin Marshall, Christian Weedbrook, John C. Howell
Mathematics, Physics, and Computer Science Faculty Articles and Research
We show how weak nonlinearities can be used in a device-independent quantum key distribution (QKD) protocol using generalized two-mode Schrödinger cat states. The QKD protocol is therefore shown to be secure against collective attacks and for some coherent attacks. We derive analytical formulas for the optimal values of the Bell parameter, the quantum bit error rate, and the device-independent secret key rate in the noiseless lossy bosonic channel. Additionally, we give the filters and measurements which achieve these optimal values. We find that, over any distance in this channel, the quantum bit error rate is identically zero, in principle, and …
Qubit Measurement Error From Coupling With A Detuned Neighbor In Circuit Qed, Mostafa Khezri, Justin Dressel, Alexander N. Korotkov
Qubit Measurement Error From Coupling With A Detuned Neighbor In Circuit Qed, Mostafa Khezri, Justin Dressel, Alexander N. Korotkov
Mathematics, Physics, and Computer Science Faculty Articles and Research
In modern circuit QED architectures, superconducting transmon qubits are measured via the state-dependent phase and amplitude shift of a microwave field leaking from a coupled resonator. Determining this shift requires integrating the field quadratures for a nonzero duration, which can permit unwanted concurrent evolution. Here we investigate such dynamical degradation of the measurement fidelity caused by a detuned neighboring qubit. We find that in realistic parameter regimes, where the qubit ensemble-dephasing rate is slower than the qubit-qubit detuning, the joint qubit-qubit eigenstates are better discriminated by measurement than the bare states. Furthermore, we show that when the resonator leaks much …
Device-Independent Relativistic Quantum Bit Commitment, Emily Adlam, Adrian Kent
Device-Independent Relativistic Quantum Bit Commitment, Emily Adlam, Adrian Kent
Mathematics, Physics, and Computer Science Faculty Articles and Research
We examine the possibility of device-independent relativistic quantum bit commitment, introducing three relativistic quantum bit commitment schemes that offer device-independent security against hypothetical postquantum adversaries subject only to the no-signaling principle. We discuss the potential threat of location attacks, in which the behavior of untrusted devices used in relativistic quantum cryptography depends on their space-time location and show that our protocols are secure against both location attacks and memory attacks. The protocols are compared to a relativistic classical bit commitment scheme with similar features and we note some advantages for the quantum schemes.
Comment On "Role Of Potentials In The Aharonov-Bohm Effect", Yakir Aharonov, Eliahu Cohen, Daniel Rohrlich
Comment On "Role Of Potentials In The Aharonov-Bohm Effect", Yakir Aharonov, Eliahu Cohen, Daniel Rohrlich
Mathematics, Physics, and Computer Science Faculty Articles and Research
Are the electromagnetic scalar and vector potentials dispensable? Vaidman [Phys. Rev. A 86, 040101(R) (2012)] has suggested that local interactions of gauge-invariant quantities, e.g., magnetic torques, suffice for the description of all quantum electromagnetic phenomena. We analyze six thought experiments that challenge this suggestion. All of them have explanations in terms of local interactions of gauge-dependent quantities, and, in addition, some have explanations in terms of nonlocal interactions of gauge-invariant quantities. We claim, however, that two of our examples have no gauge-invariant formal description and that, in general, no local description can dispense with electromagnetic potentials.
Shifting The Quantum-Classical Boundary: Theory And Experiment For Statistically Classical Optical Fields, Xiao-Feng Qian, Bethany Little, John C. Howell, Joseph H. Eberly
Shifting The Quantum-Classical Boundary: Theory And Experiment For Statistically Classical Optical Fields, Xiao-Feng Qian, Bethany Little, John C. Howell, Joseph H. Eberly
Mathematics, Physics, and Computer Science Faculty Articles and Research
The growing recognition that entanglement is not exclusively a quantum property, and does not even originate with Schrödinger’s famous remark about it [Proc. Cambridge Philos. Soc. 31, 555 (1935)], prompts the examination of its role in marking the quantum-classical boundary. We have done this by subjecting correlations of classical optical fields to new Bell-analysis experiments and report here values of the Bell parameter greater than ℬ=2.54. This is many standard deviations outside the limit ℬ=2 established by the Clauser–Horne–Shimony–Holt Bell inequality [Phys. Rev. Lett. 23, 880 (1969)], in agreement with our theoretical classical prediction, and not far from the Tsirelson …
How To Measure Magnetic Flux With A Single Position Measurement?, Eliahu Cohen, Lev Vaidman, Yakir Aharonov
How To Measure Magnetic Flux With A Single Position Measurement?, Eliahu Cohen, Lev Vaidman, Yakir Aharonov
Mathematics, Physics, and Computer Science Faculty Articles and Research
Current methods for measuring magnetic flux are based on performing many measurements over a large ensemble of electrons. We propose a novel method based on wave function "revival" for measuring the flux modulo using only a single electron. A preliminary analysis of the feasibility of the experiment is provided.
Spacetime Algebra As A Powerful Tool For Electromagnetism, Justin Dressel, Konstantin Y. Bliokh, Franco Nori
Spacetime Algebra As A Powerful Tool For Electromagnetism, Justin Dressel, Konstantin Y. Bliokh, Franco Nori
Mathematics, Physics, and Computer Science Faculty Articles and Research
We present a comprehensive introduction to spacetime algebra that emphasizes its practicality and power as a tool for the study of electromagnetism. We carefully develop this natural (Clifford) algebra of the Minkowski spacetime geometry, with a particular focus on its intrinsic (and often overlooked) complex structure. Notably, the scalar imaginary that appears throughout the electromagnetic theory properly corresponds to the unit 4-volume of spacetime itself, and thus has physical meaning. The electric and magnetic fields are combined into a single complex and frame-independent bivector field, which generalizes the Riemann-Silberstein complex vector that has recently resurfaced in studies of the single …
Violating The Modified Helstrom Bound With Nonprojective Measurements, Justin Dressel, Todd A. Brun, Alexander N. Korotkov
Violating The Modified Helstrom Bound With Nonprojective Measurements, Justin Dressel, Todd A. Brun, Alexander N. Korotkov
Mathematics, Physics, and Computer Science Faculty Articles and Research
We consider the discrimination of two pure quantum states with three allowed outcomes: a correct guess, an incorrect guess, and a nonguess. To find an optimum measurement procedure, we define a tunable cost that penalizes the incorrect guess and nonguess outcomes. Minimizing this cost over all projective measurements produces a rigorous cost bound that includes the usual Helstrom discrimination bound as a special case.We then show that nonprojective measurements can outperform this modified Helstrom bound for certain choices of cost function. The Ivanovic-Dieks-Peres unambiguous state discrimination protocol is recovered as a special case of this improvement.Notably, while the cost advantage …
Can A Future Choice Affect A Past Measurement's Outcome?, Yakir Aharonov, Eliahu Cohen, Avshalom C. Elitzur
Can A Future Choice Affect A Past Measurement's Outcome?, Yakir Aharonov, Eliahu Cohen, Avshalom C. Elitzur
Mathematics, Physics, and Computer Science Faculty Articles and Research
An EPR experiment is studied where each particle within the entangled pair undergoes a few weak measurements (WMs) along some pre-set spin orientations, with the outcomes individually recorded. Then the particle undergoes one strong measurement along an orientation chosen at the last moment. Bell-inequality violation is expected between the two final measurements within each EPR pair. At the same time, statistical agreement is expected between these strong measurements and the earlier weak ones performed on that pair. A contradiction seemingly ensues: (i) Bell’s theorem forbids spin values to exist prior to the choice of the orientation measured; (ii) A weak …
Heisenberg Scaling With Weak Measurement: A Quantum State Discrimination Point Of View, Andrew N. Jordan, Jeff Tollaksen, James E. Troupe, Justin Dressel, Yakir Aharonov
Heisenberg Scaling With Weak Measurement: A Quantum State Discrimination Point Of View, Andrew N. Jordan, Jeff Tollaksen, James E. Troupe, Justin Dressel, Yakir Aharonov
Mathematics, Physics, and Computer Science Faculty Articles and Research
We examine the results of the paper “Precision metrology using weak measurements” (Zhang et al. arXiv:1310.5302, 2013) from a quantum state discrimination point of view. The Heisenberg scaling of the photon number for the precision of the interaction parameter between coherent light and a spin one-half particle (or pseudo-spin) has a simple interpretation in terms of the interaction rotating the quantum state to an orthogonal one. To achieve this scaling, the information must be extracted from the spin rather than from the coherent state of light, limiting the applications of the method to phenomena such as cross-phase modulation. …
Weak Values As Interference Phenomena, Justin Dressel
Weak Values As Interference Phenomena, Justin Dressel
Mathematics, Physics, and Computer Science Faculty Articles and Research
Weak values arise experimentally as conditioned averages of weak (noisy) observable measurements that minimally disturb an initial quantum state, and also as dynamical variables for reduced quantum state evolution even in the absence of measurement. These averages can exceed the eigenvalue range of the observable ostensibly being estimated, which has prompted considerable debate regarding their interpretation. Classical conditioned averages of noisy signals only show such anomalies if the quantity being measured is also disturbed prior to conditioning. This fact has recently been rediscovered, along with the question whether anomalous weak values are merely classical disturbance effects. Here we carefully review …
Four Tails Problems For Dynamical Collapse Theories, Kelvin J. Mcqueen
Four Tails Problems For Dynamical Collapse Theories, Kelvin J. Mcqueen
Philosophy Faculty Articles and Research
The primary quantum mechanical equation of motion entails that measurements typically do not have determinate outcomes, but result in superpositions of all possible outcomes. Dynamical collapse theories (e.g. GRW) supplement this equation with a stochastic Gaussian collapse function, intended to collapse the superposition of outcomes into one outcome. But the Gaussian collapses are imperfect in a way that leaves the superpositions intact. This is the tails problem. There are several ways of making this problem more precise. But many authors dismiss the problem without considering the more severe formulations. Here I distinguish four distinct tails problems. The first (bare tails …
Weak Values Obtained In Matter-Wave Interferometry, Stephan Sponar, Tobias Denkmayr, Hermann Geppert, Hartmutt Lemmel, Alexandre Matzkin, Jeff Tollaksen, Yuji Hasegawa
Weak Values Obtained In Matter-Wave Interferometry, Stephan Sponar, Tobias Denkmayr, Hermann Geppert, Hartmutt Lemmel, Alexandre Matzkin, Jeff Tollaksen, Yuji Hasegawa
Mathematics, Physics, and Computer Science Faculty Articles and Research
Weak values, introduced more than 25 years ago, underwent a metamorphosis from a theoretical curiosity to a powerful resource in photonics for exploring foundations of quantum mechanics, as well as a practical laboratory tool. Due to the tiny coherence volume of particles used in matter-wave optics, a straightforward implementation of weak measurements is not feasible. We have overcome this hurdle by developing a method to weakly measure a massive particle's spin component. A neutron optical approach is realized by utilizing neutron interferometry, where the neutron's spin is coupled weakly to its spatial degree of freedom. Here, we present how one …
Fundamental Mathematics Of Consciousness, Menas Kafatos
Fundamental Mathematics Of Consciousness, Menas Kafatos
Mathematics, Physics, and Computer Science Faculty Articles and Research
We explore a mathematical formalism that ties together the observer with the observed in the view that Consciousness is primary, operating through three principles which apply at all levels, the essence of qualia of experience. The formalism is a simplified version of Hilbert space mathematics encountered in quantum mechanics. It does, however, go beyond specific interpretations of quantum mechanics and has strong philosophical foundations in Western philosophy as well as monistic systems of the East. The implications are explored and steps for the full development of this axiomatic mathematical approach to Consciousness are discussed.
Logical Pre- And Post-Selection Paradoxes Are Proofs Of Contextuality, Matthew F. Pusey, Matthew S. Leifer
Logical Pre- And Post-Selection Paradoxes Are Proofs Of Contextuality, Matthew F. Pusey, Matthew S. Leifer
Mathematics, Physics, and Computer Science Faculty Articles and Research
If a quantum system is prepared and later post-selected in certain states, “paradoxical” predictions for intermediate measurements can be obtained. This is the case both when the intermediate measurement is strong, i.e. a projective measurement with Lüders-von Neumann update rule, or with weak measurements where they show up in anomalous weak values. Leifer and Spekkens [Phys. Rev. Lett. 95, 200405] identified a striking class of such paradoxes, known as logical pre- and postselection paradoxes, and showed that they are indirectly connected with contextuality. By analysing the measurement-disturbance required in models of these phenomena, we find that the strong measurement version …