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Quantum Information Theory

Quantum Metropolis sampling

Wed, 2011-03-02 10:04 - Lukas Theussl
Date: 
2011-03-02
Author(s): 

K. Temme, T. J. Osborne, K. G. Vollbrecht, D. Poulin & F. Verstraete

Reference: 

Nature 471, 87–90 (03 March 2011), doi:10.1038/nature09770

URL: 

http://www.nature.com/nature/journal/v471/n7336/full/nature09770.html

Metropolis algorithm is the standard method for the simulation of interacting particles on classical computers. In this work, the authors demonstrate how to implement a quantum version of the Metropolis algorithm on a quantum computer. This algorithm permits to sample directly from the eigenstates of the Hamiltonian and thus evades the sign problem present in classical simulations. A small scale implementation of this algorithm can already be achieved with today's technology.

Defect center room-temperature quantum processors

Thu, 2011-02-17 16:28 - Daniel Rudolph
Date: 
2010-05-25
Author(s): 

J. Wrachtrup

Reference: 

Proceedings of the National Academy of Sciences of the United States of America 107, 9479-9480 (21)

URL: 

http://www.pnas.org/content/107/21/9479.extract

Quantum information devices promise unique opportunities in information technology. Physicists are intrigued with building such devices because they probe our understanding of the nature of quantum mechanics. Quantum effects, although providing the basis of atomic, molecular, and solid state physics, usually are not observed in everyday life because the highly fragile nature of coherence and entanglement requires extensive shielding against environmental effects.

Low-dimensional quite noisy bound entanglement with a cryptographic key

Thu, 2011-02-17 14:10 - Q-Essence Coordinator
Date: 
2010-12-13
Reference: 

Łukasz Pankowski and Michał Horodecki
J. Phys. A: Math. Theor. 44 035301 (2011)
DOI: 10.1088/1751-8113/44/3/035301

We provide a class of bound entangled states that have a positive distillable secure key rate. The smallest state of this kind is 4otimes4. Our class is a generalization of the class presented in Horodecki et al (2008 IEEE Trans. Inf. Theory 54 2621–5).

Phase estimation without a priori phase knowledge in the presence of loss

Thu, 2011-02-17 13:00 - Q-Essence Coordinator
Date: 
2010-11-04
Reference: 

Jan Kołodyński and Rafał Demkowicz-Dobrzański
Phys. Rev. A 82, 053804 (2010)
http://link.aps.org/doi/10.1103/PhysRevA.82.053804

We find the optimal scheme for quantum phase estimation in the presence of loss when no a priori knowledge on the estimated phase is available. We prove analytically an explicit lower bound on estimation uncertainty, which shows that, as a function of the number of probes, quantum precision enhancement amounts at most to a constant factor improvement over classical strategies.

 

Practical private database queries based on a quantum-key-distribution protocol

Thu, 2011-02-17 12:26 - Q-Essence Coordinator
Date: 
2011-02-02
Author(s): 

Markus Jakobi, Christoph Simon, Nicolas Gisin, Jean-Daniel Bancal, Cyril Branciard, Nino Walenta, and Hugo Zbinden

Reference: 

Phys. Rev. A 83, 022301 (2011)

URL: 

http://link.aps.org/doi/10.1103/PhysRevA.83.022301

Absence of Thermalization in Nonintegrable Systems

Thu, 2011-02-17 10:22 - Q-Essence Coordinator
Date: 
2011-01-24
Author(s): 

Christian Gogolin, Markus P. Müller, and Jens Eisert

Reference: 

Phys. Rev. Lett. 106, 040401 (2011)

URL: 

http://link.aps.org/doi/10.1103/PhysRevLett.106.040401

Device-Independent Tests of Classical and Quantum Dimensions

Wed, 2011-02-16 18:16 - Q-Essence Coordinator
Date: 
2010-11-30
Author(s): 

Rodrigo Gallego, Nicolas Brunner, Christopher Hadley, and Antonio Acín

Reference: 

Phys. Rev. Lett. 105, 230501 (2010)

URL: 

http://link.aps.org/doi/10.1103/PhysRevLett.105.230501

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