PRL: General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

Low-Noise Amplification of a Continuous-Variable Quantum State

R. C. Pooser, A. M. Marino, V. Boyer, K. M. Jones, and P. D. Lett — 2009-06-29T00:00:00-04:00

Author(s): R. C. Pooser, A. M. Marino, V. Boyer, K. M. Jones, and P. D. Lett
We present an experimental realization of a low-noise, phase-insensitive optical amplifier using a four-wave mixing interaction in hot Rb vapor. Performance near the quantum limit for a range of amplifier gains, including near unity, can be achieved. Such low-noise amplifiers are essential for so-ca...
[Phys. Rev. Lett. 103, 010501] Published Mon Jun 29, 2009

Broadcast Copies Reveal the Quantumness of Correlations

M. Piani, M. Christandl, C. E. Mora, and P. Horodecki — 2009-06-25T00:00:00-04:00

Author(s): M. Piani, M. Christandl, C. E. Mora, and P. Horodecki
We study the quantumness of bipartite correlations by proposing a quantity that combines a measure of total correlations—mutual information—with the notion of broadcast copies—i.e., generally nonfactorized copies—of bipartite states. By analyzing how our quantity increases with the number of...
[Phys. Rev. Lett. 102, 250503] Published Thu Jun 25, 2009

Heralded Quantum Gate between Remote Quantum Memories

P. Maunz, S. Olmschenk, D. Hayes, D. N. Matsukevich, L.-M. Duan, and C. Monroe — 2009-06-25T00:00:00-04:00

Author(s): P. Maunz, S. Olmschenk, D. Hayes, D. N. Matsukevich, L.-M. Duan, and C. Monroe
We demonstrate a probabilistic entangling quantum gate between two distant trapped ytterbium ions. The gate is implemented between the hyperfine “clock” state atomic qubits and mediated by the interference of two emitted photons carrying frequency encoded qubits. Heralded by the coincidence dete...
[Phys. Rev. Lett. 102, 250502] Published Thu Jun 25, 2009

Tripartite Entanglement versus Tripartite Nonlocality in Three-Qubit Greenberger-Horne-Zeilinger-Class States

S. Ghose, N. Sinclair, S. Debnath, P. Rungta, and R. Stock — 2009-06-25T00:00:00-04:00

Author(s): S. Ghose, N. Sinclair, S. Debnath, P. Rungta, and R. Stock
We analyze the relationship between tripartite entanglement and genuine tripartite nonlocality for three-qubit pure states in the Greenberger-Horne-Zeilinger class. We consider a family of states known as the generalized Greenberger-Horne-Zeilinger states and derive an analytical expression relating...
[Phys. Rev. Lett. 102, 250404] Published Thu Jun 25, 2009

Time-Symmetric Quantum Theory of Smoothing

Mankei Tsang — 2009-06-25T00:00:00-04:00

Author(s): Mankei Tsang
Smoothing is an estimation technique that takes into account both past and future observations and can be more accurate than filtering alone. In this Letter, a quantum theory of smoothing is constructed using a time-symmetric formalism, thereby generalizing prior work on classical and quantum filter...
[Phys. Rev. Lett. 102, 250403] Published Thu Jun 25, 2009

Minimal Energy Cost for Thermodynamic Information Processing: Measurement and Information Erasure

Takahiro Sagawa and Masahito Ueda — 2009-06-24T00:00:00-04:00

Author(s): Takahiro Sagawa and Masahito Ueda
The fundamental lower bounds on the thermodynamic energy cost of measurement and information erasure are determined. The lower bound on the erasure validates Landauer’s principle for a symmetric memory; for other cases, the bound indicates the breakdown of the principle. Our results constitute the...

[Phys. Rev. Lett. 102, 250602] Published Wed Jun 24, 2009

All Entangled States are Useful for Channel Discrimination

Marco Piani and John Watrous — 2009-06-24T00:00:00-04:00

Author(s): Marco Piani and John Watrous
We prove that every entangled state is useful as a resource for the problem of minimum-error channel discrimination. More specifically, given a single copy of an arbitrary bipartite entangled state, it holds that there is an instance of a quantum channel discrimination task for which this state allo...
[Phys. Rev. Lett. 102, 250501] Published Wed Jun 24, 2009

Inelastic Collisions of a Fermi Gas in the BEC-BCS Crossover

X. Du, Y. Zhang, and J. E. Thomas — 2009-06-24T00:00:00-04:00

Author(s): X. Du, Y. Zhang, and J. E. Thomas
We measure inelastic three-body and two-body collisional decay rates for a two-component Fermi gas of ^{6} Li, which are highly suppressed by the Pauli exclusion principle. Our measurements are made in the BEC-BCS crossover regime, near the two-body collisional (Feshbach) resonance. At high temperat...
[Phys. Rev. Lett. 102, 250402] Published Wed Jun 24, 2009

Test of the Additivity Principle for Current Fluctuations in a Model of Heat Conduction

Pablo I. Hurtado and Pedro L. Garrido — 2009-06-23T00:00:00-04:00

Author(s): Pablo I. Hurtado and Pedro L. Garrido
The additivity principle allows to compute the current distribution in many one-dimensional (1D) nonequilibrium systems. Using simulations, we confirm this conjecture in the 1D Kipnis-Marchioro-Presutti model of heat conduction for a wide current interval. The current distribution shows both Gaussia...
[Phys. Rev. Lett. 102, 250601] Published Tue Jun 23, 2009

Hydrodynamic View of Wave-Packet Interference: Quantum Caves

2009-06-22T00:00:00-04:00

Author(s): Chia-Chun Chou, Ángel S. Sanz, Salvador Miret-Artés, and Robert E. Wyatt
Wave-packet interference is investigated within the complex quantum Hamilton-Jacobi formalism using a hydrodynamic description. Quantum interference leads to the formation of the topological structure of quantum caves in space-time Argand plots. These caves consist of the vortical and stagnation tub...
[Phys. Rev. Lett. 102, 250401] Published Mon Jun 22, 2009

Microcanonical Phase Diagrams of Short-Range Ferromagnets

Michael Kastner and Michel Pleimling — 2009-06-19T00:00:00-04:00

Author(s): Michael Kastner and Michel Pleimling
A phase diagram is a graph in parameter space showing the phase boundaries of a many-particle system. Commonly, the control parameters are chosen to be those of the (generalized) canonical ensemble, such as temperature and magnetic field. However, depending on the physical situation of interest, the...
[Phys. Rev. Lett. 102, 240604] Published Fri Jun 19, 2009

Matrix Product States for Dynamical Simulation of Infinite Chains

M. C. Bañuls, M. B. Hastings, F. Verstraete, and J. I. Cirac — 2009-06-18T00:00:00-04:00

Author(s): M. C. Bañuls, M. B. Hastings, F. Verstraete, and J. I. Cirac
We propose a new method for computing the ground state properties and the time evolution of infinite chains based on a transverse contraction of the tensor network. The method does not require finite size extrapolation and avoids explicit truncation of the bond dimension along the evolution. By fold...
[Phys. Rev. Lett. 102, 240603] Published Thu Jun 18, 2009

Longest Excursion of Stochastic Processes in Nonequilibrium Systems

Claude Godrèche, Satya N. Majumdar, and Grégory Schehr — 2009-06-18T00:00:00-04:00

Author(s): Claude Godrèche, Satya N. Majumdar, and Grégory Schehr
We consider the excursions, i.e., the intervals between consecutive zeros, of stochastic processes that arise in a variety of nonequilibrium systems and study the temporal growth of the longest one l_{max⁡} (t) up to time t. For smooth processes, we find a universal linear growth ⟨l_{max⁡} (t)...
[Phys. Rev. Lett. 102, 240602] Published Thu Jun 18, 2009

Atom Interferometers with Scalable Enclosed Area

Holger Müller, Sheng-wey Chiow, Sven Herrmann, and Steven Chu — 2009-06-18T00:00:00-04:00

Author(s): Holger Müller, Sheng-wey Chiow, Sven Herrmann, and Steven Chu
Bloch oscillations (i.e., coherent acceleration of matter waves by an optical lattice) and Bragg diffraction are integrated into light-pulse atom interferometers with large momentum splitting between the interferometer arms, and hence enhanced sensitivity. Simultaneous acceleration of both arms in t...
[Phys. Rev. Lett. 102, 240403] Published Thu Jun 18, 2009

Large Momentum Beam Splitter Using Bloch Oscillations

2009-06-18T00:00:00-04:00

Author(s): Pierre Cladé, Saïda Guellati-Khélifa, François Nez, and François Biraben
The sensitivity of an inertial sensor based on an atomic interferometer is proportional to the velocity separation of atoms in the two arms of the interferometer. In this Letter we describe how Bloch oscillations can be used to increase this separation and to create a large momentum transfer (LMT) b...
[Phys. Rev. Lett. 102, 240402] Published Thu Jun 18, 2009

Efficient Multiparticle Entanglement via Asymmetric Rydberg Blockade

M. Saffman and K. Mølmer — 2009-06-17T00:00:00-04:00

Author(s): M. Saffman and K. Mølmer
We present an efficient method for producing N particle entangled states using Rydberg blockade interactions. Optical excitation of Rydberg states that interact weakly, yet have a strong coupling to a second control state is used to achieve state dependent qubit rotations in small ensembles. On the ...
[Phys. Rev. Lett. 102, 240502] Published Wed Jun 17, 2009

Supersonic Quantum Communication

J. Eisert and D. Gross — 2009-06-17T00:00:00-04:00

Author(s): J. Eisert and D. Gross
When locally exciting a quantum lattice model, the excitation will propagate through the lattice. This effect is responsible for a wealth of nonequilibrium phenomena, and has been exploited to transmit quantum information. It is a commonly expressed belief that for local Hamiltonians, any such propa...
[Phys. Rev. Lett. 102, 240501] Published Wed Jun 17, 2009

Determination of the Newtonian Gravitational Constant G with Time-of-Swing Method

2009-06-16T00:00:00-04:00

Author(s): Jun Luo, Qi Liu, Liang-Cheng Tu, Cheng-Gang Shao, Lin-Xia Liu, Shan-Qing Yang, Qing Li, and Ya-Ting Zhang
We present a new value of the Newtonian gravitational constant G by using the time-of-swing method. Several improvements greatly reduce the uncertainties: (1) measuring the anelasticity of the fiber directly; (2) using spherical source masses minimizes the effects of density inhomogeneity and ecce...
[Phys. Rev. Lett. 102, 240801] Published Tue Jun 16, 2009

Unpredictable Tunneling of a Classical Wave-Particle Association

A. Eddi, E. Fort, F. Moisy, and Y. Couder — 2009-06-16T00:00:00-04:00

Author(s): A. Eddi, E. Fort, F. Moisy, and Y. Couder
A droplet bouncing on a vibrated bath becomes a “walker” moving at constant velocity on the interface when it couples to the surface wave it generates. Here the motion of a walker is investigated when it collides with barriers of various thicknesses. Surprisingly, it undergoes a form of tunnelin...
[Phys. Rev. Lett. 102, 240401] Published Tue Jun 16, 2009

Critical Behavior and Scaling in Trapped Systems

Massimo Campostrini and Ettore Vicari — 2009-06-15T00:00:00-04:00

Author(s): Massimo Campostrini and Ettore Vicari
We study the scaling properties of critical particle systems confined by a potential. Using renormalization-group arguments, we show that their critical behavior can be cast in the form of a trap-size scaling, resembling finite-size scaling theory, with a nontrivial trap critical exponent θ, which ...

[Phys. Rev. Lett. 102, 240601] Published Mon Jun 15, 2009

Qubit Residence Time Measurements with a Bose-Einstein Condensate

D. Sokolovski — 2009-06-12T00:00:00-04:00

Author(s): D. Sokolovski
We show that an electrostatic qubit located near a Bose-Einstein condensate trapped in a symmetric double-well potential can be used to measure the duration the qubit has spent in one of its quantum states. The strong, medium, and weak measurement regimes are analyzed. The analogy between the reside...
[Phys. Rev. Lett. 102, 230405] Published Fri Jun 12, 2009

Unifying All Classical Spin Models in a Lattice Gauge Theory

G. De las Cuevas, W. Dür, H. J. Briegel, and M. A. Martin-Delgado — 2009-06-11T00:00:00-04:00

Author(s): G. De las Cuevas, W. Dür, H. J. Briegel, and M. A. Martin-Delgado
The partition function of all classical spin models, including all discrete standard statistical models and all Abelian discrete lattice gauge theories (LGTs), is expressed as a special instance of the partition function of the 4D Z_{2} LGT. This unifies all classical spin models with apparently ver...
[Phys. Rev. Lett. 102, 230502] Published Thu Jun 11, 2009

Casimir Interaction between Plane and Spherical Metallic Surfaces

2009-06-11T00:00:00-04:00

Author(s): Antoine Canaguier-Durand, Paulo A. Maia Neto, Ines Cavero-Pelaez, Astrid Lambrecht, and Serge Reynaud
We give an exact series expansion of the Casimir force between plane and spherical metallic surfaces in the nontrivial situation where the sphere radius R, the plane-sphere distance L and the plasma wavelength λ_{P} have arbitrary relative values. We then present numerical evaluation of this expans...
[Phys. Rev. Lett. 102, 230404] Published Thu Jun 11, 2009

Quantum Teleportation of the Temporal Fluctuations of Light

Changsuk Noh, A. Chia, Hyunchul Nha, M. J. Collett, and H. J. Carmichael — 2009-06-10T00:00:00-04:00

Author(s): Changsuk Noh, A. Chia, Hyunchul Nha, M. J. Collett, and H. J. Carmichael
A scheme for the teleportation of a beam of light including its temporal fluctuations is proposed. Expressions for the teleported degrees of first- and second-order optical coherence are presented. Teleportation of an antibunched photon stream illustrates the proposal.
[Phys. Rev. Lett. 102, 230501] Published Wed Jun 10, 2009

Reduction and Possible Elimination of Coating Thermal Noise Using a Rigidly Controlled Cavity with a Quantum-Nondemolition Technique

Kentaro Somiya — 2009-06-09T00:00:00-04:00

Author(s): Kentaro Somiya
Thermal noise of a mirror is one of the most important issues in high-precision measurements such as gravitational-wave detection or cold damping experiments. It has been pointed out that thermal noise of a mirror with multilayer coatings can be reduced by mechanical separation of the layers. In th...
[Phys. Rev. Lett. 102, 230801] Published Tue Jun 09, 2009

Positron Kinetics in Soft Condensed Matter

R. D. White and R. E. Robson — 2009-06-09T00:00:00-04:00

Author(s): R. D. White and R. E. Robson
We outline a new kinetic theory for positrons in soft matter, which blends together cross sections for positrons scattering from single molecules, with the structure function of the medium as a whole. Numerical results are presented for positrons in liquid argon, where negative differential conducti...
[Phys. Rev. Lett. 102, 230602] Published Tue Jun 09, 2009

ac-Driven Atomic Quantum Motor

A. V. Ponomarev, S. Denisov, and P. Hänggi — 2009-06-08T00:00:00-04:00

Author(s): A. V. Ponomarev, S. Denisov, and P. Hänggi
We propose an ac-driven quantum motor consisting of two different, interacting ultracold atoms placed into a ring-shaped optical lattice and submerged in a pulsating magnetic field. While the first atom carries a current, the second one serves as a quantum starter. For fixed zero-momentum initial co...
[Phys. Rev. Lett. 102, 230601] Published Mon Jun 08, 2009

Ferrofluidity in a Two-Component Dipolar Bose-Einstein Condensate

Hiroki Saito, Yuki Kawaguchi, and Masahito Ueda — 2009-06-08T00:00:00-04:00

Author(s): Hiroki Saito, Yuki Kawaguchi, and Masahito Ueda
It is shown that the interface in a two-component Bose-Einstein condensate (BEC) with a dipole-dipole interaction spontaneously develops patterns similar to those formed in a ferrofluid. Hexagonal, labyrinthine, solitonlike structures, and hysteretic behavior are numerically demonstrated. Superflow ...
[Phys. Rev. Lett. 102, 230403] Published Mon Jun 08, 2009

Observation of Fermi Polarons in a Tunable Fermi Liquid of Ultracold Atoms

André Schirotzek, Cheng-Hsun Wu, Ariel Sommer, and Martin W. Zwierlein — 2009-06-08T00:00:00-04:00

Author(s): André Schirotzek, Cheng-Hsun Wu, Ariel Sommer, and Martin W. Zwierlein
We have observed Fermi polarons, dressed spin-down impurities in a spin-up Fermi sea of ultracold atoms. The polaron manifests itself as a narrow peak in the impurities’ rf spectrum that emerges from a broad incoherent background. We determine the polaron energy and the quasiparticle residue for v...

[Phys. Rev. Lett. 102, 230402] Published Mon Jun 08, 2009

Occupation Statistics of a Bose-Einstein Condensate for a Driven Landau-Zener Crossing

2009-06-08T00:00:00-04:00

Author(s): Katrina Smith-Mannschott, Maya Chuchem, Moritz Hiller, Tsampikos Kottos, and Doron Cohen
We consider an atomic Bose-Einstein condensate loaded in a biased double-well trap with tunneling rate K and interatomic interaction U. The Bose-Einstein condensate is prepared such that all N atoms are in the left well. We drive the system by sweeping the potential difference E between the two well...
[Phys. Rev. Lett. 102, 230401] Published Mon Jun 08, 2009