We derive universal relations for the rf spectroscopy of a two-dimensional Fermi gas consisting of two spin states interacting through an S-wave scattering length. The rf transition rate has a high-frequency tail that is proportional to the contact and displays logarithmic scaling violations, decrea...

[Phys. Rev. Lett. 108, 060402] Published Thu Feb 09, 2012

We investigate the ground states of a Bose-Einstein condensate of indirect excitons coupled to an electron gas. We show that in a properly designed system the crossing of a roton minimum into the negative energy domain can result in the appearance of the supersolid phase, characterized by periodicit...

[Phys. Rev. Lett. 108, 060401] Published Thu Feb 09, 2012

We introduce a new scheme for continuous-variable entanglement distillation that requires only linear temporal and constant physical or spatial resources. Distillation is the process by which high-quality entanglement may be distributed between distant nodes of a network in the unavoidable presence ...

[Phys. Rev. Lett. 108, 060502] Published Wed Feb 08, 2012

We characterize the entanglement contained in a pure three-qubit state via operational entanglement measures. To this end, we derive a new decomposition for arbitrary three-qubit states which is characterized by five parameters (up to local unitary operations). We show that these parameters are uniq...

[Phys. Rev. Lett. 108, 060501] Published Wed Feb 08, 2012

The effect of particle-nonconserving processes on the steady state of driven diffusive systems is studied within the context of a generalized ABC model. It is shown that in the limit of slow nonconserving processes, the large deviation function of the overall particle density can be computed by maki...

[Phys. Rev. Lett. 108, 060602] Published Tue Feb 07, 2012

We demonstrate that a large ensemble of noiseless globally coupled-pinned oscillators is capable of rectifying spatial disorder with spontaneous current activated through a dynamical phase transition mechanism, either of first or second order, depending on the profile of the pinning potential. In th...

[Phys. Rev. Lett. 108, 060601] Published Tue Feb 07, 2012

We propose a practical entanglement classification scheme for general multipartite pure states in arbitrary dimensions under local unitary equivalence by exploiting the high order singular value decomposition technique and local symmetries of the states. By virtue of this scheme, the method of deter...

[Phys. Rev. Lett. 108, 050501] Published Tue Jan 31, 2012

A classical one-time pad allows two parties to send private messages over a public classical channel—an eavesdropper who intercepts the communication learns nothing about the message. A quantum one-time pad is a shared quantum state which allows two parties to send private messages or private quantu...

[Phys. Rev. Lett. 108, 040504] Published Fri Jan 27, 2012

A linear optical quantum computer relies on interference between photonic qubits for logic, and entanglement for near-deterministic operation. Here we measure the interference and entanglement properties of photons emitted by a quantum dot embedded within a light-emitting diode. We show that pairs o...

[Phys. Rev. Lett. 108, 040503] Published Fri Jan 27, 2012

We study analytically the order statistics of a time series generated by the positions of a symmetric random walk of n steps with step lengths of finite variance σ². We show that the statistics of the gap d_k,n=M_k,n-M_k+1,n between the kth and the (k+1)th maximum of the time series becomes stationary,...

[Phys. Rev. Lett. 108, 040601] Published Thu Jan 26, 2012

Superactivation is the property that two channels with zero quantum capacity can be used together to yield a positive capacity. Here we demonstrate that this effect exists for a wide class of inequivalent channels, none of which can simulate each other. We also consider the case where one of two zer...

[Phys. Rev. Lett. 108, 040501] Published Wed Jan 25, 2012

We consider Bell tests involving bipartite states shared between three parties. We show that the simple inclusion of a third part may greatly simplify the measurement scenario (in terms of the number of measurement settings per part) and allows the identification of previously unknown nonlocal resou...

[Phys. Rev. Lett. 108, 040402] Published Wed Jan 25, 2012

Teleportation of a quantum state may be used for distributing entanglement between distant qubits in quantum communication and for quantum computation. Here we demonstrate the implementation of a teleportation protocol, up to the single-shot measurement step, with superconducting qubits coupled to a...

[Phys. Rev. Lett. 108, 040502] Published Tue Jan 24, 2012

We derive the general form of a master equation describing the reduced time evolution of a sequence of subsystems “propagating” in an environment which can be described as a sequence of subenvironments. The interaction between subsystems and subenvironments is described in terms of a collision model...

[Phys. Rev. Lett. 108, 040401] Published Tue Jan 24, 2012

For genuine nonequilibrium states that even at fixed external control parameter exhibit dissipation, we extend the Hatano-Sasa equality to processes with feedback control. The resulting bound on the maximal extractable work is substantially sharper than what would follow from applying the Sagawa-Ued...

[Phys. Rev. Lett. 108, 030601] Published Thu Jan 19, 2012

We present a formalism to derive entanglement criteria beyond the Gaussian regime that can be readily tested by only homodyne detection. The measured observable is the Einstein-Podolsky-Rosen (EPR) correlation. Its arbitrary functional form enables us to detect non-Gaussian entanglement even when an...

[Phys. Rev. Lett. 108, 030503] Published Thu Jan 19, 2012

An approach to fast entanglement generation based on Rydberg dephasing of collective excitations (spin waves) in large, optically thick atomic ensembles is proposed. Long-range 1/r³ atomic interactions are induced by microwave mixing of opposite-parity Rydberg states. The required long coherence tim...

[Phys. Rev. Lett. 108, 030501] Published Thu Jan 19, 2012

Entanglement and nonlocality are both fundamental aspects of quantum theory, and play a prominent role in quantum information science. The exact relation between entanglement and nonlocality is, however, still poorly understood. Here we make progress in this direction by showing that, contrary to wh...

[Phys. Rev. Lett. 108, 030403] Published Thu Jan 19, 2012

We propose a new methodology, namely, the “quantum Zeno blockade,” for managing light scattering at a few-photon level in general nonlinear-optical media, such as crystals, fibers, silicon microrings, and atomic vapors. Using this tool, antibunched emission of photon pairs can be achieved, leading t...

[Phys. Rev. Lett. 108, 030502] Published Wed Jan 18, 2012

Quantum contextuality, as proved by Kochen and Specker, and also by Bell, should manifest itself in any state in any system with more than two distinguishable states and recently has been experimentally verified. However, for the simplest system capable of exhibiting contextuality, a qutrit, the qua...

[Phys. Rev. Lett. 108, 030402] Published Wed Jan 18, 2012

Sequences of alternating-sign time-dependent electric field pulses lead to coherent interference effects in Schwinger vacuum pair production, producing a Ramsey interferometer, an all-optical time-domain realization of the multiple-slit interference effect, directly from the quantum vacuum. The inte...

[Phys. Rev. Lett. 108, 030401] Published Wed Jan 18, 2012

We present a particle separation mechanism which induces the motion of particles of different sizes in opposite directions. The mechanism is based on the combined action of a driving force and an entropic rectification of the Brownian fluctuations caused by the asymmetric form of the channel along w...

[Phys. Rev. Lett. 108, 020604] Published Fri Jan 13, 2012

We demonstrate theoretically and experimentally the phenomenon of vibrational resonance in a periodic potential, using cold atoms in an optical lattice as a model system. A high-frequency (HF) drive, with a frequency much larger than any characteristic frequency of the system, is applied by phase mo...

[Phys. Rev. Lett. 108, 020603] Published Fri Jan 13, 2012

The first characterization of mixed-state entanglement was achieved for two-qubit states in Werner’s seminal work [ Phys. Rev. A 40 4277 (1989)]. A physically important extension concerns mixtures of a pure entangled state [such as the Greenberger-Horne-Zeilinger (GHZ) state] and the unpolarized st...

[Phys. Rev. Lett. 108, 020502] Published Fri Jan 13, 2012

The dynamics of a dimer coupled to two different environments, each in a spin star configuration under the influence of decoherence, is studied. The exact analytical expression for the transition probability in the dimer system is obtained for different situations, i.e., independent and correlated e...

[Phys. Rev. Lett. 108, 020602] Published Wed Jan 11, 2012

Distillation of entanglement using only Gaussian operations is an important primitive in quantum communication, quantum repeater architectures, and distributed quantum computing. Existing distillation protocols for continuous degrees of freedom are only known to converge to a Gaussian state when mea...

[Phys. Rev. Lett. 108, 020501] Published Wed Jan 11, 2012

We present a stochastic approach to nonequilibrium thermodynamics based on the expression of the entropy production rate advanced by Schnakenberg for systems described by a master equation. From the microscopic Schnakenberg expression we get the macroscopic bilinear form for the entropy production r...

[Phys. Rev. Lett. 108, 020601] Published Tue Jan 10, 2012

Quantum walk represents one of the most promising resources for the simulation of physical quantum systems, and has also emerged as an alternative to the standard circuit model for quantum computing. Here we investigate how the particle statistics, either bosonic or fermionic, influences a two-parti...

[Phys. Rev. Lett. 108, 010502] Published Thu Jan 05, 2012

The graph-theoretic Ramsey numbers are notoriously difficult to calculate. In fact, for the two-color Ramsey numbers R(m,n) with m, n≥3, only nine are currently known. We present a quantum algorithm for the computation of the Ramsey numbers R(m,n). We show how the computation of R(m,n) can be mapped...

[Phys. Rev. Lett. 108, 010501] Published Thu Jan 05, 2012

We investigate theoretically the phase diagram of a spin-orbit coupled Bose gas in two-dimensional harmonic traps. We show that at strong spin-orbit coupling the single-particle spectrum decomposes into different manifolds separated by ℏω_⊥, where ω_⊥ is the trapping frequency. For a weakly interactin...

[Phys. Rev. Lett. 108, 010402] Published Wed Jan 04, 2012