| |
Lutz, T., Kolenderski, P., & Jennewein, T. (2013). Toward a downconversion source of positively spectrally correlated and decorrelated telecom photon pairs. Opt. Lett., 38(5), 697–699.
Abstract: Frequency correlation (or decorrelation) of photon pairs is of great importance in long-range quantum communications and photonic quantum computing. We experimentally characterize a spontaneous parametric downconversion source, based on a beta-barium borate crystal cut for type-II phase matching at 1550 nm, which has the capability to emit photons with positive or no spectral correlations. Our system employs a carefully designed detection method exploiting two InGaAs detectors. (C) 2013 Optical Society of America
|
|
Vermeyden, L., Bonsma, M., Noel, C., Donohue, J. M., Wolfe, E., & Resch, K. J. (2013). Experimental violation of three families of Bell's inequalities. Phys. Rev. A, 87(3), 5 pp.
Abstract: Bell's inequalities are important to our understanding of quantum foundations and critical to several quantum technologies. Arecentwork [E. Wolfe and S. F. Yelin, Phys. Rev. A86, 012123 (2012)] derived three parametrized families of two-particle, two-setting Bell inequalities. These inequalities are important as they theoretically explore a larger volume of allowed quantum correlations over local hidden-variable models than previous results [A. Cabello, Phys. Rev. A 72, 012113 (2005)] by exploiting marginal, or single particle measurements. In this work we subject those predictions to experimental test using nonmaximally entangled photon pairs to optimize the expected violation. We find excellent agreement with the upper bounds predicted by quantum mechanics with violations of the limits imposed by local hidden-variable models as large as almost 30 sigma for the optimal parameters and a significant violation over a wide range of parameters. DOI: 10.1103/PhysRevA.87.032105
|
|
Meyer-Scott, E., Roy, V., Bourgoin, J. P., Higgins, B. L., Shalm, L. K., & Jennewein, T. (2013). Generating polarization-entangled photon pairs using cross-spliced birefringent fibers. Opt. Express, 21(5), 6205–6212.
Abstract: We demonstrate a novel polarization-entangled photon-pair source based on standard birefringent polarization-maintaining optical fiber. The source consists of two stretches of fiber spliced together with perpendicular polarization axes, and has the potential to be fully fiber-based, with all bulk optics replaced with in-fiber equivalents. By modelling the temporal walk-off in the fibers, we implement compensation necessary for the photon creation processes in the two stretches of fiber to be indistinguishable. Our source subsequently produces a high quality entangled state having (92.2 +/- 0.2) % fidelity with a maximally entangled Bell state. (c) 2013 Optical Society of America
|
|
Johnston, N., Skowronek, L., & Stormer, E. (2013). Generation of mapping cones from small sets. Linear Alg. Appl., 438(7), 3062–3075.
Abstract: We answer in the affirmative a recently-posed question that asked if there exists an “untypical” convex mapping cone – i.e., one that does not arise from the transpose map and the cones of k-positive and k-superpositive maps. We explicitly construct such a cone based on atomic positive maps. Our general technique is to consider the smallest convex mapping cone generated by a single map, and we derive several results on such mapping cones. We use this technique to also present several other examples of untypical mapping cones, including a family of cones generated by spin factors. We also provide a full characterization of mapping cones generated by single elements in the qubit case in terms of their typicality. (C) 2012 Elsevier Inc. All rights reserved.
Keywords: Mapping cones; Positive maps; Entanglement
|
|
Brodutch, A., Datta, A., Modi, K., Rivas, A., & Rodriguez-Rosario, C. A. (2013). Vanishing quantum discord is not necessary for completely positive maps. Phys. Rev. A, 87(4), 5 pp.
Abstract: The description of the dynamics of a system that may be correlated with its environment is only meaningful within the context of a specific framework. Different frameworks rely upon different assumptions about the initial system-environment state. We reexamine the connections between complete positivity and quantum discord within two different sets of assumptions about the relevant family of initial states. We present an example of a system-environment state with nonvanishing quantum discord that leads to a completely positive map. This invalidates an earlier claim about the necessity of vanishing quantum discord for completely positive maps. In our final remarks, we discuss the physical validity of each approach. DOI: 10.1103/PhysRevA.87.042301
|
|
Mazurek, M. D., Schreiter, K. M., Prevedel, R., Kaltenbaek, R., & Resch, K. J. (2013). Dispersion-cancelled biological imaging with quantum-inspired interferometry. Sci Rep, 3, 5 pp.
Abstract: Quantum information science promises transformative impact over a range of key technologies in computing, communication, and sensing. A prominent example uses entangled photons to overcome the resolution-degrading effects of dispersion in the medical-imaging technology, optical coherence tomography. The quantum solution introduces new challenges: inherently low signal and artifacts, additional unwanted signal features. It has recently been shown that entanglement is not a requirement for automatic dispersion cancellation. Such classical techniques could solve the low-signal problem, however they all still suffer from artifacts. Here, we introduce a method of chirped-pulse interferometry based on shaped laser pulses, and use it to produce artifact-free, high-resolution, dispersion-cancelled images of the internal structure of a biological sample. Our work fulfills one of the promises of quantum technologies: automatic-dispersion-cancellation interferometry in biomedical imaging. It also shows how subtle differences between a quantum technique and its classical analogue may have unforeseen, yet beneficial, consequences.
|
|
Johansson, J. R., Johansson, G., Wilson, C. M., Delsing, P., & Nori, F. (2013). Nonclassical microwave radiation from the dynamical Casimir effect. Phys. Rev. A, 87(4), 6 pp.
Abstract: We investigate quantum correlations in microwave radiation produced by the dynamical Casimir effect in a superconducting waveguide terminated and modulated by a superconducting quantum interference device. We apply nonclassicality tests and evaluate the entanglement for the predicted field states. For realistic circuit parameters, including thermal background noise, the results indicate that the produced radiation can be strictly nonclassical and can have a measurable amount of intermode entanglement. If measured experimentally, these nonclassicality indicators could give further evidence of the quantum nature of the dynamical Casimir radiation in these circuits. DOI: 10.1103/PhysRevA.87.043804
|
|
Jiang, Z., Piani, M., & Caves, C. M. (2013). Ancilla models for quantum operations: for what unitaries does the ancilla state have to be physical? Quantum Inf. Process., 12(5), 1999–2017.
Abstract: Any evolution described by a completely positive trace-preserving linear map can be imagined as arising from the interaction of the evolving system with an initially uncorrelated ancilla. The interaction is given by a joint unitary operator, acting on the system and the ancilla. Here we study the properties such a unitary operator must have in order to force the choice of a physical-that is, positive-state for the ancilla if the end result is to be a physical-that is, completely positive-evolution of the system.
Keywords: Ancilla model; Stinespring extension; Completely positive; Quantum operation; Quantum tomography
|
|
Graydon, M. A. (2013). Quaternionic Quantum Dynamics on Complex Hilbert Spaces. Found. Phys., 43(5), 656–664.
Abstract: We consider a quaternionic quantum formalism for the description of quantum states and quantum dynamics. We prove that generalized quantum measurements on physical systems in quaternionic quantum theory can be simulated by usual quantum measurements with positive operator valued measures on complex Hilbert spaces. Furthermore, we prove that quaternionic quantum channels can be simulated by completely positive trace preserving maps on complex matrices. These novel results map all quaternionic quantum processes to algorithms in usual quantum information theory.
Keywords: Quantum foundations; Quaternions; Division rings; Born rule; Quaternionic POVMs; Quaternionic quantum channels
|
|
|
Martín-Martínez, E., Hosler, D., & Montero, M. (2012). Fundamental limitations to information transfer in accelerated frames. PRA, 86(6), 062307.
|
|
|
Martín-Martínez, E., Montero, M., & del Rey, M. (2013). Wavepacket detection with the Unruh-DeWitt model. PRD, 87(6), 064038.
|
|
|
Brown, E. G., Martín-Martínez, E., Menicucci, N. C., & Mann, R. B. (2013). Detectors for probing relativistic quantum physics beyond perturbation theory. PRD, 87(8), 084062.
|
|
|
Martín-Martínez, E., Aasen, D., & Kempf, A. (2013). Processing Quantum Information with Relativistic Motion of Atoms. PRL, 110(16), 160501.
|
|
Serbyn, M., & Abanin, D. A. (2013). New Dirac points and multiple Landau level crossings in biased trilayer graphene. Phys. Rev. B, 87(11), 10 pp.
Abstract: Recently a new high-mobility Dirac material, trilayer graphene, was realized experimentally. The band structure of ABA-stacked trilayer graphene consists of a monolayer-like and a bilayer-like pair of bands. Here we study electronic properties of ABA-stacked trilayer graphene biased by a perpendicular electric field. We find that the combination of the bias and trigonal warping gives rise to a set of new Dirac points: In each valley, seven species of Dirac fermions with small masses of order of a few meV emerge. The positions and masses of the emergent Dirac fermions are tunable by bias, and one group of Dirac fermions becomes massless at a certain bias value. Therefore, in contrast to bilayer graphene, the conductivity at the neutrality point is expected to show nonmonotonic behavior, becoming of the order of a few e(2)/h when some Dirac masses vanish. Further, we analyze the evolution of the Landau level spectrum as a function of bias. The emergence of new Dirac points in the band structure translates into new threefold-degenerate groups of Landau levels. This leads to an anomalous quantum Hall effect, in which some quantum Hall steps have a height of 3e(2)/h. At an intermediate bias, the degeneracies of all Landau levels get lifted, and in this regime all quantum Hall plateaus are spaced by e(2)/h. Finally, we show that the pattern of Landau level crossings is very sensitive to certain band structure parameters, and can therefore provide a useful tool for determining their precise values. DOI: 10.1103/PhysRevB.87.115422
|
|
Jochym-O'Connor, T., Yu, Y. F., Helou, B., & Laflamme, R. (2013). THE ROBUSTNESS OF MAGIC STATE DISTILLATION AGAINST ERRORS IN CLIFFORD GATES. Quantum Inform. Comput., 13(5-6), 361–378.
Abstract: Quantum error correction and fault-tolerance have provided the possibility for large scale quantum computations without a detrimental loss of quantum information. A very natural class of gates for fault-tolerant quantum computation is the Clifford gate set and as such their usefulness for universal quantum computation is of great interest. Clifford group gates augmented by magic state preparation give the possibility of simulating universal quantum computation. However, experimentally one cannot expect to perfectly prepare magic states. Nonetheless, it has been shown that by repeatedly applying operations from the Clifford group and measurements in the Pauli basis, the fidelity of noisy prepared magic states can be increased arbitrarily close to a pure magic state [1]. We investigate the robustness of magic state distillation to perturbations of the initial states to arbitrary locations in the Bloch sphere due to noise. Additionally, we consider a depolarizing noise model on the quantum gates in the decoding section of the distillation protocol and demonstrate its effect on the convergence rate and threshold value. Finally, we establish that faulty magic state distillation is more efficient than fault-tolerance-assisted magic state distillation at low error rates due to the large overhead in the number of quantum gates and qubits required in a fault-tolerance architecture. The ability to perform magic state distillation with noisy gates leads us to conclude that this could be a realistic scheme for future small-scale quantum computing devices as fault-tolerance need only be used in the final steps of the protocol.
Keywords: Universal quantum computation; magic state distillation; quantum fault-tolerance
|
|
|
