Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session U27: Quantum Entanglement: Theory and Experiment |
Hide Abstracts |
Sponsoring Units: GQI Chair: Andrews Doherty, University of Sydney Room: 329 |
Thursday, March 21, 2013 11:15AM - 11:27AM |
U27.00001: Positivity of Partial Transpose and Separability of Dicke state mixtures Elie Wolfe, Susanne Yelin We study mixtures of permutation symmetric (Dicke) states, with a special focus on superradiance time evolution. For such systems we develop necessary separability criteria for general N-qubit systems based on the condition of Positive Partial Transpose. We also compose sufficient separability criteria for the specific cases of two and three qubits. Comparing the criteria we prove that, for Dicke state mixtures, the PPT test is always sufficient to imply full separability. [Preview Abstract] |
Thursday, March 21, 2013 11:27AM - 11:39AM |
U27.00002: Polynomial invariants to quantify Four-body Correlations Santosh Shelly Sharma, Naresh Kumar Sharma Local unitary invariance and notion of negativity fonts are used as the principle tools to construct four qubit polynomial invariants of degree 8, 12, and 24. Determinants of negativity fonts are linked to matrices obtained from state operator through selective partial transposition. Our general aim is to construct the polynomial invariants that quantify entanglement due to $K-$body correlations in an $N$-qubit ($N?K$) pure state. This is done by constructing N-qubit invariants from multivariate forms with ($K-1$)-qubit invariants as coefficients. In particular, the invariant that quantifies entanglement due to $N$-body correlations is obtained from a biform having as coefficients the $N-1$ qubit invariants. A polynomial invariant that is non-zero on four qubit pure states with four-body correlations and zero on all other states, is identified. Classification of four qubit states into seven major classes, using criterion based on the nature of correlations, is discussed. [Preview Abstract] |
Thursday, March 21, 2013 11:39AM - 11:51AM |
U27.00003: Numerical Calculations of the Three Tangle for Mixed States Samuel Rodriques, Peter Love We present a steepest descent convex roof optimization algorithm, using the Cayley parametrization of the unitary group, which can be used to calculate the convex roof of any entanglement monotone on mixed states. We use the algorithm to calculate the three tangle on a set of states for which the tangle is known analytically, and show that our results are in good agreement with the analytical calculations. We then randomly generate a set of full-rank three qubit states, of varied mixedness and tangle, calculate the tangle on these states using our convex roof algorithm, and also calculate the lower bound on the three-tangle which has been provided by Eltschka and Siewert[1]. We thus provide a profile of the strength of the Eltschka-Siewert bound, as a function of mixedness and tangle. [1] ``Optimal Witnesses for Three Qubit Entanglement from Greenberger-Horne-Zeilinger Symmetry,'' Eltschka, C. and Siewert, J., forthcoming.~arXiv: 1204.5451 [Preview Abstract] |
Thursday, March 21, 2013 11:51AM - 12:03PM |
U27.00004: Quantum steering ellipsoids: The way to represent two qubits Sania Jevtic, Matthew Pusey, David Jennings, Terry Rudolph A single qubit state is faithfully represented as a vector in the Bloch sphere. A two qubit state may be faithfully represented as two vectors and a quantum steering ellipsoid (QSE) in the Bloch sphere. When Alice and Bob share a pair of qubits, the QSE is the geometric set of states that Bob can steer Alice's qubit to when he implements all possible measurements on his qubit. We argue that the QSE is the way one should visualise a two qubit state and show how the correlative properties of the state manifest themselves in this paradigm, in particular we give simple conditions for when the state is entangled, or has discord. We will also present novel features of the two qubit state that are revealed by the QSE formalism, and show that a state corresponding to an ellipsoid with non-zero volume contains a new type of correlation. Such a state is a useful resource in a game where Bob succeeds if he can steer Alice's qubit to three states with linearly independent Bloch vectors. [Preview Abstract] |
Thursday, March 21, 2013 12:03PM - 12:15PM |
U27.00005: Quantum Discord Bounds the Amount of Distributed Entanglement Marco Piani, Tan Kok Chuan, Jean Maillard, Kavan Modi, Tomasz Paterek, Mauro Paternostro The ability to distribute quantum entanglement is a prerequisite for many fundamental tests of quantum theory and numerous quantum information protocols. Two distant parties can increase the amount of entanglement between them by means of quantum communication encoded in a carrier that is sent from one party to the other. Intriguingly, entanglement can be increased even when the exchanged carrier is not entangled with the parties. However, in light of the defining property of entanglement stating that it cannot increase under classical communication, the carrier must be quantum. Here we show that, in general, the increase of relative entropy of entanglement between two remote parties is bounded by the amount of nonclassical correlations of the carrier with the parties as quantified by the relative entropy of discord. We study implications of this bound, provide new examples of entanglement distribution via unentangled states, and put further limits on this phenomenon. [Preview Abstract] |
Thursday, March 21, 2013 12:15PM - 12:27PM |
U27.00006: Topological Classification of Types of Quantum Discord Evolutions Nga Nguyen, Robert Joynt Quantum discord is a type of quantum correlation that has recently attracted extensive attention. One question that is of experimental importance is how quantum correlations such as entanglement and discord are erased by external noise. A general classification of time evolution is seen to depend essentially on the understanding of the topology of the set $C$ of concordant (zero-discord) states. In the 2-qubit case, we show that $C$ is a 9-dimensional simply-connected manifold with boundary that can be embedded in the 15-dimensional space of 2-qubit density matrices. This yields 6 topologically distinct categories for the joint time evolution of entanglement and discord that exhaust all possibilities. We show that these 6 categories can be obtained in one physical model using independent or correlated random telegraph noise sources in the Markovian regime. Transition between these categories is of topological nature and is governed by changing physical parameters or initial conditions. [Preview Abstract] |
Thursday, March 21, 2013 12:27PM - 12:39PM |
U27.00007: Mutual Preservation of Entanglement Andrzej Veitia We study a generalized double Jaynes-Cummings (JC) model where two entangled pairs of two-level atoms interact indirectly. We focus on the case where the cavities and the entangled pairs are uncorrelated. We show that there exist initial states of the qubit system so that two entangled pairs are available at all times. In particular, the minimum entanglement in the pairs as a function of the initial state is studied. Finally, we extend our findings to a model consisting of multi-mode atom-cavity interactions. We use a non-Markovian quantum state diffusion (QSD) equation to obtain the steady-state density matrix for the qubits. We show that the multi-mode model also displays dynamical preservation of entanglement. [Preview Abstract] |
Thursday, March 21, 2013 12:39PM - 12:51PM |
U27.00008: Quantum geometry and entanglement in the Rabi model Justin Wilson, Victor Galitski In composite systems, entanglement can be useful for control since one system's properties become fundamentally linked with another system's properties. One way of measuring entanglement is with a quantity called I-concurrence, a generalization of concurrence to systems that have more states than a qubit. We show that I-concurrence can be rewritten in terms of quantum geometric quantities. In particular, we show a dependence on the Hilbert-Schmidt distance measure on the Hilbert space of one of the subsystems. Using this quantity and the recently exactly solved Rabi model, we calculate the entanglement between eigenstates in the Rabi model. [Preview Abstract] |
Thursday, March 21, 2013 12:51PM - 1:03PM |
U27.00009: Classical Analogs of Quantum Entanglement Brian La Cour Quantum computing algorithms rely upon entanglement and context-based measurements, properties that are well exhibited by atomic or photonic systems. In some cases, these properties can be mimicked by cleverly contrived classical systems. We present a notional scheme for such classical analogs and compare their predictions to those of an associated quantum system. Entanglement is verified operationally using quantum tomography, wherein the quantum mixed state is inferred from measurements on a complete orthonormal set of Hermitian observables. Using the Peres-Horodecki criterion for separability, we examine the partial transpose of the estimated density matrix to establish a necessary, and in some cases sufficient, condition for entanglement. Through the use of Monte Carlo simulations, we find that certain classical systems do indeed exhibit a measurably significant level of entanglement. [Preview Abstract] |
Thursday, March 21, 2013 1:03PM - 1:15PM |
U27.00010: Robust distant-entanglement generation using coherent multiphoton scattering Ching-Kit Chan, L. J. Sham The generation and controllability of entanglement between distant quantum states have been the heart of quantum computation and quantum information processing. Existing schemes for solid state qubit entanglement are based on the single-photon spectroscopy that has the merit of a high fidelity entanglement creation, but with a very limited efficiency. This severely restricts the scalability for a qubit network system. Here, we describe a new distant entanglement protocol using coherent multiphoton scattering. The scheme makes use of the postselection of large and distinguishable photon signals, and has both a high success probability and a high entanglement fidelity. Our result shows that the entanglement generation is robust against photon fluctuations, and has an average entanglement duration within the decoherence time in various qubit systems, based on existing experimental parameters. [Preview Abstract] |
Thursday, March 21, 2013 1:15PM - 1:27PM |
U27.00011: Optical control of entangled states in semiconductor quantum wells Mario Borunda, Esa Rasanen, Thomas Blasi, Eric Heller The ability to coherently control arbitrary two-electron states, and to maximize the entanglement, opens up further perspectives in solid-state quantum information. In this talk, we present theory and calculations for coherent high-fidelity quantum control of many-particle states in semiconductor quantum wells. We have shown that coupling a two-electron double quantum dot to a terahertz optical source enables targeted excitations that are one to two orders of magnitude faster and significantly more accurate than those obtained with electric gates. The optical fields subject to realistic physical constraints are obtained through quantum optimal control theory that is applied in conjunction with the numerically exact solution of the time-dependent Schrodinger equation. [Preview Abstract] |
Thursday, March 21, 2013 1:27PM - 1:39PM |
U27.00012: Persistent Quantum Beats and Long-Distance Entanglement from Waveguide-Mediated Interactions Huaixiu Zheng, Harold U. Baranger We study photon-photon correlations and entanglement generation in a one-dimensional waveguide coupled to two qubits with an arbitrary spatial separation [1]. Such a system can be realized by coupling a 1D open transmission line to superconducting qubits. To treat the combination of nonlinear elements and 1D continuum, we develop a novel Green function method. The vacuum-mediated qubit-qubit interactions cause quantum beats to appear in the second-order correlation function. We go beyond the Markovian regime and observe that such quantum beats persist much longer than the qubit lifetime. A high degree of long-distance entanglement can be generated, increasing the potential of waveguide-QED systems for scalable quantum networking. [1] H. Zheng, and H. U. Baranger, arXiv:1206.4442 (2012). [Preview Abstract] |
Thursday, March 21, 2013 1:39PM - 1:51PM |
U27.00013: PPLN Device Characterization and Novel Entanglement Schemes Sean Krupa, Eric Stinaff, David Nippa, Lee Oesterling Bright sources of entangled photons are of great interest in the quantum information community, and the non-linear optical process of Spontaneous Parametric Downconversion (SPDC) is a well-known means to create entangled photons. Additionally, periodic polling has emerged as a viable choice for quasi-phase matching the downconverted photons rendering them useful for experimentation. Periodically Poled Lithium Niobate (PPLN) is among the best choices for these materials as it optically robust, temperature tunable, and commercially available. The addition of waveguide structures in PPLN devices not only increase its viability as a source of entangled photons but can also become an integral part of the entanglement schemes as well. Thorough characterization of PPLN devices is essential for the optimization of SPDC and their use to create entangled states. We will report characterization results for wave-guided PPLN devices including: waveguide geometry, fiber coupling efficiency, polling period details, and downconversion efficiency. Of particular interest is our device's ability to be used for novel entanglement states involving one or more waveguides. [Preview Abstract] |
Thursday, March 21, 2013 1:51PM - 2:03PM |
U27.00014: Measurement of the joint spectrum of entangled photons using rotary dispersion Daniel Jones, Todd Pittman We report a new method of observing the spectral entanglement of photons generated in spontaneous parametric down-conversion (PDC). In contrast to previous methods based on spatial or temporal dispersion, our method is based on rotary dispersion and polarization measurements. Our experiment utilizes a variation of the S\'{e}narmont compensator in order to rotate the polarization state of the entangled signal and idler photons. By passing the photons through several stages of these ``rotators,'' we essentially create a Lyot filter in which we can directly correlate an analyzer measurement after the rotators with a specific wavelength, within a resolution defined by the theory. This method is fundamentally different than previous experiments to measure the joint spectrum of PDC photons because of the periodicity of using analyzers as the measurement devices. The periodicity of the analyzers causes a trade-off between the resolution of the device and the maximum bandwidth of the entangled photons that can be measured. [Preview Abstract] |
Thursday, March 21, 2013 2:03PM - 2:15PM |
U27.00015: Realistic loophole-free Bell test with atom-photon entanglement Colin Teo, Mateus Ara\'{u}jo, Marco Quintino, Ji\v{r}\'{I} Min\'{a}\v{r}, Daniel Cavalcanti, Valerio Scarani, Marcelo Terra Cunha, Marcelo Santos The establishment of nonlocal correlations, guaranteed through the violation of a Bell inequality, is not only important from a fundamental point of view, but constitutes the basis for device-independent quantum information technologies. Although several nonlocality tests have been performed so far, all of them suffered from either the locality or the detection loopholes. Recent studies have suggested that the use of atom-photon entanglement can lead to Bell inequality violations with moderate transmission and detection efficiencies. In this paper we propose an experimental setup realizing a simple atom-photon entangled state that, under realistic experimental parameters available to date, achieves a significant violation of the Clauser-Horn-Shimony-Holt Bell inequality. Most importantly, the violation remains when considering typical detection efficiencies and losses due to required propagation distances. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700