01.40.+n Entanglement as a resource for information processing

Single-photon interference due to motion in an atomic collective excitation

Date: 
2016-12-19
Author(s): 

Daniel J. Whiting, Nikola Šibalić, James Keaveney, Charles S. Adams, and Ifan G. Hughes

Reference: 

arXiv:1612.05467v1

Quantum-state engineering is of critical importance to the development of quantum technologies. One promising platform is thermal atomic vapours, because they offer long coherence times with reproducible and scalable hardware. However, the inability to address isolated atomic states in a controlled manner, due to multi-level degeneracy and motional broadening, is a major obstacle to their wider application.

Non-equilibrium phase-transitions in multi-component Rydberg gases

Date: 
2016-06-29
Author(s): 

D. S. Ding, C. S. Adams, B. S. Shi, G. C. Guo

Reference: 

arXiv:1606.08791v1 [physics.atom-ph]

URL: 

arXiv:1606.08791v1

Highly-excited Rydberg atoms have strong long-range interactions resulting in exotic optical properties such as large single photon non-linearities and intrinsic bistability. In this paper we study optical-driven non-equilibrium phase transitions in a thermal Rydberg gas with a sensitivity two order of magnitude higher than in previous work.

Information Theoretical Analysis of Quantum Optimal Control

Date: 
2014-07-02
Author(s): 

S. Lloyd and S. Montangero

Reference: 

Phys. Rev. Lett. 113, 010502 (2014)
http://dx.doi.org/10.1103/PhysRevLett.113.010502

We study the relations between classical information and the feasibility of accurate manipulation of quantum system dynamics. We show that if an efficient classical representation of the dynamics exists, optimal control problems on many-body quantum systems can be solved efficiently with finite precision. In particular, one-dimensional slightly entangled dynamics can be efficiently controlled. We provide a bound for the minimal time necessary to perform the optimal process given the bandwidth of the control pulse, which is the continuous version of the Solovay-Kitaev theorem.

Noise-resistant optimal spin squeezing via quantum control

Date: 
2016-01-27
Author(s): 

T. Pichler, T. Caneva, S. Montangero, M. D. Lukin, and T. Calarco

Reference: 

Phys. Rev. A 93, 013851 (2016)
http://dx.doi.org/10.1103/PhysRevA.93.013851

Entangled atomic states, such as spin-squeezed states, represent a promising resource for a new generation of quantum sensors and atomic clocks. We demonstrate that optimal control techniques can be used to substantially enhance the degree of spin squeezing in strongly interacting many-body systems, even in the presence of noise and imperfections. Specifically, we present a protocol that is robust to noise and outperforms conventional methods. Potential experimental implementations are discussed.

Approximating Gibbs states of local Hamiltonians efficiently with PEPS

Date: 
2015-01-29
Author(s): 

A. Molnár, N. Schuch, F. Verstraete, J. I. Cirac

Reference: 

Phys. Rev. B, 91, 045138 (2015)

We analyze the error of approximating Gibbs states of local quantum spin Hamiltonians on lattices with Projected Entangled Pair States (PEPS) as a function of the bond dimension (D), temperature (&#946;&#8722;1), and system size (N). First, we introduce a compression method in which the bond dimension scales as D=eO(log2(N/&#1013;)) if &#946;<O(log(N)).

Area laws and approximations of quantum many-body states

Date: 
2015-05-26
Author(s): 

Yimin Ge, Jens Eisert

Reference: 

arXiv:1411.2995

It is commonly believed that area laws for entanglement entropies imply that a quantum many-body state can be faithfully represented by efficient tensor network states - a conjecture frequently stated in the context of numerical simulations and analytical considerations. In this work, we show that this is in general not the case, except in one dimension.

A quantum gate between a flying optical photon and a single trapped atom

Date: 
2014-04-09
Author(s): 

Andreas Reiserer, Norbert Kalb, Gerhard Rempe, Stephan Ritter

Reference: 

Nature 508, 237 (2014)

The steady increase in control over individual quantum systems has backed the dream of a quantum technology that provides functionalities beyond any classical device. Two particularly promising applications have been explored during the past decade: First, photon-based quantum communication, which guarantees unbreakable encryption but still has to be scaled to high rates over large distances. Second, quantum computation, which will fundamentally enhance computability if it can be scaled to a large number of quantum bits.

Extracting entanglement from identical particles

Date: 
2013-12-16
Author(s): 

N. Killoran, M. Cramer and M. B. Plenio

Reference: 

Physical Review Letters 112, 150501 (2014)

Identical particles and entanglement are both fundamental components of quantum mechanics. However, when identical particles are condensed in a single spatial mode, the standard notions of entanglement, based on clearly identifiable subsystems, break down. This has led many to conclude that such systems have limited value for quantum information tasks, compared to distinguishable particle systems.

Toward protocols for quantum-ensured privacy and secure voting

Date: 
2011-08-24
Author(s): 

Marianna Bonanome, Vladimir Buzek, Mark Hillery, and Mario Ziman

Reference: 

Phys. Rev. A 84, 022331 (2011)

We present a number of schemes that use quantum mechanics to preserve privacy, in particular, we show that entangled quantum states can be useful in maintaining privacy. We further develop our original proposal [see M. Hillery, M. Ziman, V. Buek and M. Bieliková Phys. Lett. A 349 75 (2006)] for protecting privacy in voting, and examine its security under certain types of attacks, in particular dishonest voters and external eavesdroppers. A variation of these quantum-based schemes can be used for multiparty function evaluation.

Coherence of large-scale entanglement

Date: 
2011-03-23
Author(s): 

T. Monz, P. Schindler, J.T. Barreiro, M. Chwalla, D. Nigg, W.A. Coish, M. Harlander, W. Hänsel, M. Hennrich, R. Blatt

Reference: 

arXiv:1009.6126

We report the creation of Greenberger-Horne-Zeilinger states with up to 14 qubits. By investigating the coherence of up to 8 ions over time, we observe a decay proportional to the square of the number of qubits. The observed decay agrees with a theoretical model which assumes a system affected by correlated, Gaussian phase noise. This model holds for the majority of current experimental systems developed towards quantum computation and quantum metrology.

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