Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session B38: Focus Session: Quantum Foundations and Technologies I |
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Sponsoring Units: GQI Chair: Matthew Pusey, Perimeter Institute for Theoretical Physics Room: 212B |
Monday, March 2, 2015 11:15AM - 11:51AM |
B38.00001: Understanding Nature from Experimental Observations: A Theory Independent Test for Gravitational Decoherence Invited Speaker: Stephanie Wehner Quantum mechanics and the theory of gravity are presently not compatible. A particular question is whether gravity causes decoherence - an unavoidable source of noise. Several models for gravitational decoherence have been proposed, not all of which can be described quantum mechanically. In parallel, several experiments have been proposed to test some of these models, where the data obtained by such experiments is analyzed assuming quantum mechanics. Since we may need to modify quantum mechanics to account for gravity, however, one may question the validity of using quantum mechanics as a calculational tool to draw conclusions from experiments concerning gravity. Here we use ideas from quantum information to propose an experiment to estimate gravitational decoherence whose conclusions hold even if quantum mechanics would need to be modified. We first establish a general information-theoretic notion of decoherence which reduces to the standard measure within quantum mechanics. Second, drawing on ideas from quantum information, we propose a very general protocol that allows us to estimate decoherence of any physical process for any physical theory satisfying only very mild conditions. Finally, we propose a concrete experiment using optomechanics to estimate gravitational decoherence in any such theoy, including quantum mechanics as a special case. Our work raises the interesting question whether other properties of nature could similarly be established from experimental observations alone - that is, without already having a rather well formed theory of nature like quantum mechanics to make sense of experimental data. We conclude by discussing this possibility. \\[4pt] Joint work with C. Pfister, J. Kaniewski, M. Tomamichel, A. Mantri, R. Schmucker and G. Milburn [Preview Abstract] |
Monday, March 2, 2015 11:51AM - 12:03PM |
B38.00002: A loophole-free Bell test with spin qubits in diamond Anais Dreau, Bas Hensen, Hannes Bernien, Andreas Reiserer, Just Ruitenberg, Machiel Blok, Matthew Markham, Daniel Twitchen, Stephanie Wehner, Ronald Hanson One of the most intriguing phenomena in quantum physics is the entanglement of spatially separated objects. The benchmark to prove the fundamental non-locality of remote entanglement is provided by the famous Bell's theorem. Nevertheless, all its experimental implementations to date open the door to loopholes that restrict the practical validity of this theorem., we present our latest experimental results towards the realization of a Bell test, aimed to close the detection loophole and address the locality and free-will loopholes in a single experiment. Our qubits consist of the electronic spin associated with single NV center defects in diamond. An efficient remote entanglement protocol allows us to generate entangled qubit pairs between two labs separated by 1.3 km on the TU Delft campus. The moderate time (\textless 3.5 us) required for high fidelity (\textgreater 99{\%}) qubit rotations and efficient (\textgreater 97{\%}) readout make our setup a good candidate to allow the experimental violation of Bell's inequalities between two space-like separated entangled spins without relying on the fair sampling assumption. [Preview Abstract] |
Monday, March 2, 2015 12:03PM - 12:15PM |
B38.00003: Experimental design of a loophole-free Bell test with spin qubits in diamond Bas Hensen, Hannes Bernien, Ana\"Is Dr\'eau, Andreas Reiserer, Just Ruitenberg, Machiel Blok, Stephanie Wehner, M. Markham, D. Twitchen, Ronald Hanson 50 years ago, John Bell formulated his famous theorem [1]. The outcomes of independent measurements on entangled objects can reveal strong correlations that violate Bell's inequality. Until now, all experimental implementations of Bell's test required additional assumptions, that open the door for so-called loopholes. These loopholes are particularly important in a cryptography setting where Bell violations enable fully device-independent protocols for quantum key distribution and certified generation of randomness. Here we will present the experimental design of a Bell test, aimed at closing the detection loophole and addressing the locality and free-will loopholes in a single experiment. We use two qubits associated with the electronic spin of the nitrogen-vacancy (NV) center in diamond, separated far enough to allow space-like separation between the two qubits during their measurement. The heralded nature of our remote entanglement protocol [2] and efficient qubit readout [3] allow us to use all entangled pairs, avoiding the fair-sampling assumption. Finally, the free-will loophole is addressed by the use of fast random number generators.\\[4pt] [1] J.S. Bell, Physics 1, 195-200 (1964)\\[0pt] [2] H. Bernien et al., Nature 497, 86-90 (2013)\\[0pt] [3] L. Robledo et al.,Nature 574, 477 (2011) [Preview Abstract] |
Monday, March 2, 2015 12:15PM - 12:27PM |
B38.00004: ABSTRACT WITHDRAWN |
Monday, March 2, 2015 12:27PM - 12:39PM |
B38.00005: On the Interpretation of Action as Entropy John Haller I present a governing hypothesize that self-information (in natural units) is equal to the integral of energy times time divided by the quantum of action. I solve for both the free particle case and for when the particle is in a potential and conclude that the principle of least action is a similitude of the 2nd law of thermodynamics. I show supporting examples including the two slit experiment, the minimum uncertainty Gaussian wave function, and the electron spin state and argue that a spin s particle is 2s$+$1 natural units of information. I share a history of these concepts and how thinking has evolved over the last 100$+$ years. Lastly I present how this hypothesis is able to reconcile the Bohemian and Copenhagen interpretations of quantum mechanics and shed light on the non-local debate. [Preview Abstract] |
Monday, March 2, 2015 12:39PM - 12:51PM |
B38.00006: No Drama Quantum Electrodynamics? Andrey Akhmeteli Is it possible to offer a ``no drama'' quantum electrodynamics, as simple (in principle) as classical electrodynamics -- a theory described by a system of partial differential equations (PDE) in 3+1 dimensions, but reproducing unitary evolution of a quantum field theory in the Fock space? The following results suggest an affirmative answer: 1. The scalar field can be algebraically eliminated from scalar electrodynamics. 2. After introduction of a complex 4-potential (producing the same electromagnetic field (EMF) as the standard real 4-potential), the spinor field can be algebraically eliminated from spinor electrodynamics. 3. The resulting theories describe independent evolution of EMF and can be embedded into quantum field theories. Another fundamental result: in a general case, the Dirac equation is equivalent to a 4th order PDE for just one component, which can be made real by a gauge transform. Issues related to the Bell theorem and the connection with Barut's self-field electrodynamics are discussed. A. Akhmeteli, Int'l Journal of Quantum Information, Vol. 9, Suppl., 17-26 (2011) A. Akhmeteli, Journal of Mathematical Physics, Vol. 52, 082303 (2011) A. Akhmeteli, quant-ph/1111.4630 A. Akhmeteli, European Physical Journal C, Vol. 73, 2371 (2013) (open access) [Preview Abstract] |
Monday, March 2, 2015 12:51PM - 1:03PM |
B38.00007: Quantum rewinding via phase estimation Gelo Noel Tabia In cryptography, the notion of a zero-knowledge proof was introduced by Goldwasser, Micali, and Rackoff [1]. An interactive proof system is said to be zero-knowledge if any verifier interacting with an honest prover learns nothing beyond the validity of the statement being proven. With recent advances in quantum information technologies, it has become interesting to ask if classical zero-knowledge proof systems remain secure against adversaries with quantum computers. The standard approach to show the zero-knowledge property involves constructing a simulator for a malicious verifier that can be rewinded to a previous step when the simulation fails. In the quantum setting, the simulator can be described by a quantum circuit that takes an arbitrary quantum state as auxiliary input but rewinding becomes a nontrivial issue. Watrous proposed a quantum rewinding technique in the case where the simulation's success probability is independent of the auxiliary input [2]. Here I present a more general quantum rewinding scheme that employs the quantum phase estimation algorithm. References: [1] S. Goldwasser, S. Micali, and C. Rackoff, SIAM J. Comput. 18(1) 186-208, 1989. [2] J. Watrous, SIAM J. Comput. 39(1) 25-58, 2009. [Preview Abstract] |
Monday, March 2, 2015 1:03PM - 1:15PM |
B38.00008: A Weak Value Based QKD Protocol Robust Against Detector Attacks James Troupe We propose a variation of the BB84 quantum key distribution protocol that utilizes the properties of weak values to insure the validity of the quantum bit error rate estimates used to detect an eavesdropper. The protocol is shown theoretically to be secure against recently demonstrated attacks utilizing detector blinding and control and should also be robust against all detector based hacking. Importantly, the new protocol promises to achieve this additional security without negatively impacting the secure key generation rate as compared to that originally promised by the standard BB84 scheme. Implementation of the weak measurements needed by the protocol should be very feasible using standard quantum optical techniques. [Preview Abstract] |
Monday, March 2, 2015 1:15PM - 1:27PM |
B38.00009: Quantum Collect Calling Eduardo Martin-Martinez We show that it is possible to use a massless field in the vacuum to communicate in such a way that the signal travels slower than the speed of light and such that no energy is transmitted from the sender to the receiver. Instead, the receiver has to supply a signal-dependent amount of work to switch his detector on and off. This type of signalling is related to Casimir-like interactions and it is made possible by dimension ---and curvature--- dependent subtleties of Huygens' principle. We will also discuss several implications of this effect in diverse scenarios ranging from quantum communication to Cosmology. [Preview Abstract] |
Monday, March 2, 2015 1:27PM - 1:39PM |
B38.00010: The Quantum Bernoulli Factory Howard Dale, David Jennings, Terry Rudolph Understanding the difference between quantum mechanics and classical probability theory amounts to understanding the difference between superposition and mixture. We take a classical sampling problem, the Bernoulli coin factory, and explore a quantum version of it. We find that the quantum factory can perform tasks which are impossible in the classical case. In some sense the Bernoulli factory can be considered as an alternate, although less applicable, kind of Turing machine. In this restricted setting results about quantum advantage become far easier to prove and the difference in capabilities between quantum and classical are much starker. By trying to identify which aspects of quantum theory are essential to this speed-up we can gain insight into what the necessary requirements for speed-up in conventional quantum computing are. [Preview Abstract] |
Monday, March 2, 2015 1:39PM - 1:51PM |
B38.00011: Certifying Unpredictable Randomness from Quantum Nonlocality Peter Bierhorst A device-independent quantum randomness protocol takes an initial random seed as input and then expands it in to a longer random string. It has been proven that if the initial random seed is trusted to be unpredictable, then the longer output string can also be certified to be unpredictable by an experimental violation of Bell's inequality. It has furthermore been argued that the initial random seed may not need to be truly unpredictable, but only uncorrelated to specific parts of the Bell experiment. In this work, we demonstrate rigorously that this is indeed true, under assumptions related to ``no superdeterminism/no conspiracy'' concepts along with the no-signaling assumption. So if we assume that superluminal signaling is impossible, then a loophole-free test of Bell's inequality would be able to generate provably unpredictable randomness from an input source of (potentially predictable) classical randomness. [Preview Abstract] |
Monday, March 2, 2015 1:51PM - 2:03PM |
B38.00012: Adaptive Quadrature Detection for Multicarrier Continuous-Variable Quantum Key Distribution Laszlo Gyongyosi, Sandor Imre We propose the adaptive quadrature detection for multicarrier continuous-variable quantum key distribution (CVQKD). A multicarrier CVQKD scheme uses Gaussian subcarrier continuous variables for the information conveying and Gaussian sub-channels for the transmission. The proposed multicarrier detection scheme dynamically adapts to the sub-channel conditions using a corresponding statistics which is provided by our sophisticated sub-channel estimation procedure. The sub-channel estimation phase determines the transmittance coefficients of the sub-channels, which information are used further in the adaptive quadrature decoding process. We define the technique called subcarrier spreading to estimate the transmittance conditions of the sub-channels with a theoretical error-minimum in the presence of a Gaussian noise. We introduce the terms of single and collective adaptive quadrature detection. We also extend the results for a multiuser multicarrier CVQKD scenario. We prove the achievable error probabilities, the signal-to-noise ratios, and quantify the attributes of the framework. The adaptive detection scheme allows to utilize the extra resources of multicarrier CVQKD and to maximize the amount of transmittable information. [Preview Abstract] |
Monday, March 2, 2015 2:03PM - 2:15PM |
B38.00013: Highly Efficient Long-Distance Quantum Communication: a Blueprint for Implementation Linshu Li, Sreraman Muralidharan, Jungsang Kim, Norbert Lutkenhaus, Mikhail Lukin, Liang Jiang Quantum repeaters provide a way for long distance quantum communication through optical fiber networks. Transmission losses and operation errors are two major challenges to the implementation of quantum repeaters. At each intermediate repeater station, transmission losses can be overcome using either heralded entanglement generation or quantum error correction, while operation errors can be corrected via entanglement purification or quantum error correction. Depending on the mechanisms used to correct loss and operation errors respectively, three generations of quantum repeaters have been proposed. We present a quantitative comparison of different quantum repeater schemes by evaluating the time- and qubit-resource consumed simultaneously. We can identify the most efficient scheme for given technological capabilities, which are characterized by fiber coupling efficiency, local gate fidelity, and local gate speed. Our work provides a roadmap for high-speed quantum networks across continental distances. [Preview Abstract] |
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