Physical Review A

We rederive the Schrödinger-Robertson uncertainty principle for the position and momentum of a quantum particle. Our derivation does not directly employ commutation relations, but works by reduction to an eigenvalue problem related to the harmonic oscillator, which can then be further exploited to f...

We show that hybrid local measurements combining homodyne measurements and photodetection provide violations of a Bell inequality with arbitrarily low photodetection efficiency. This is shown in two different scenarios: when one part receives an atom entangled to the field mode to be measured by the...

We show that partial transposition of any 2⊗n state can have at most (n−1) number of negative eigenvalues. This extends a decade old result of the 2⊗2 case by Sanpera et al. [ Phys. Rev. A 58 826 (1998)]. We then apply this result to critically assess an important conjecture recently made by Girola...

Recent work has examined how undecidable problems can arise in quantum-information science. We augment this by introducing three undecidable problems stated in terms of tensor networks. These relate to ideas of Penrose about the physicality of a spin network representing a physical process, closed t...

In distributed quantum information processing, flying photons entangle matter qubits confined in cavities. However, when a matter qubit is homogeneously broadened, the strong-coupling regime of cavity QED is typically required, which is hard to realize in actual experimental setups. Here, we show th...

We consider the problem of establishing a two-qubit entangled state of optimal fidelity across a noisy quantum channel when only a single use of the channel and local postprocessing by trace-preserving operations are allowed. We show that the optimal fidelity is obtained only when part of an appropr...

We propose a family of surface codes with general lattice structures, where the error tolerances against bit and phase errors can be controlled asymmetrically by changing the underlying lattice geometries. The surface codes on various lattices are found to be efficient in the sense that their thresh...

Here, we report a measurement scheme for determining an absorption profile with an accuracy imposed solely by photon shot noise. We demonstrate the power of this technique by measuring the absorption of cesium vapor with an uncertainty at the 2-ppm level. This extremely high signal-to-noise ratio al...

We characterize the two-photon excitation of an ultracold gas of rubidium atoms to Rydberg states analyzing the induced atomic losses from an optical dipole trap. Extending the duration of the Rydberg excitation to several milliseconds, the ground-state atoms are continuously coupled to the formed p...

We show that the dipole-dipole interaction between two Rydberg atoms can give rise to long-range molecules. The binding potential arises from two states that converge to different separated-atom asymptotes. These states interact weakly at large distances, but start to repel each other strongly as th...

We demonstrate the deceleration of heavy polar molecules in low-field-seeking states by combining a cryogenic source and a traveling-wave Stark decelerator. The cryogenic source provides a high-intensity beam with low speed and temperature, and the traveling-wave decelerator provides large decelerat...

We investigate theoretically the deterministic generation of quantum states with negative Wigner functions, by using giant nonlinearities due to collisional interactions between Rydberg polaritons. The state resulting from the polariton interactions may be transferred with high fidelity into a photo...

We investigate strongly correlated phases of two-component (or pseudospin-1/2) Bose gases under rapid rotation through exact diagonalization on a torus geometry. In the case of pseudospin-independent contact interactions, we find the formation of gapped spin-singlet states at the filling factors ν=k...

In a dipolar Fermi gas, the anisotropic interaction between electric dipoles can be turned into an effectively attractive interaction in the presence of a rotating electric field. We show that the topological p_x+ip_y superfluid phase can be realized in a single-component dipolar Fermi gas trapped in ...

We show that atoms in an optical lattice can respond cooperatively to resonant incident light and that such a response can be employed for precise control and manipulation of light on a subwavelength scale. Specific collective excitation modes of the system that result from strong light-mediated dip...

The ideal (i.e., noninteracting), homogeneous Fermi gas, with its characteristic sharp Fermi surface in the momentum distribution, is a fundamental concept relevant to the behavior of many systems. With trapped Fermi gases of ultracold atoms, one can realize and probe a nearly ideal Fermi gas; howev...

The gauge field of a uniform line of magnetic monopoles is created using a single Laguerre-Gauss laser mode and a gradient in the physical magnetic field. We study the effect of these monopoles on a Bose condensed atomic gas, whose vortex structure transforms when more than six monopoles are trapped...

In this Rapid Communication, we experimentally demonstrate that the signal velocity, defined as the earliest time when a signal is detected above the realistic noise floor, may be altered by a region of anomalous dispersion. We encode information in the spatial degree of freedom of an optical pulse ...

We study linear and nonlinear wave dynamics in the Lieb lattice, in the vicinity of an intersection point between two conical bands and a flat band. We define a pseudospin operator and derive a nonlinear equation for spin-1 waves, analogous to the spin-1/2 nonlinear Dirac equation. We then study the...

We present a theory of coherent propagation and energy or power transfer in a low-dimension array of coupled nonlinear waveguides. It is demonstrated that in the array with nonequal cores (e.g., with the central core) stable steady-state coherent multicore propagation is possible only in the nonline...

We calculate all the elements of the Mueller matrix for light scattering from a two-dimensional randomly rough lossy metal surface. The calculations are carried out for arbitrary angles of incidence by the use of nonperturbative numerical solutions of the reduced Rayleigh equations. We foresee that ...

Non-Hermitian Hamiltonians satisfying parity-time (PT) symmetry reveal unusual physical phenomena related to exceptional points, where the onset of PT symmetry breaking occurs. Here, by permitting dispersive variations in the PT-symmetric potential along the propagation axis of a wave, we show that ...

Transverse pattern formation in an optical cavity containing a cloud of cold two-level atoms is discussed. We show that density modulation becomes the dominant mechanism as the atomic temperature is reduced. Indeed, for low but easily achievable temperatures the internal degrees of freedom of the at...

Quasi-phase-matching in a dual gas (Ar-H₂) multijet array has recently been demonstrated to be a promising way to enhance the yield of high-order harmonics (HH). Here, we investigate the HH produced individually from these two gases under identical conditions. Our results indicate that the quasi-pha...

We describe a scheme that allows for the transfer of a quantum state between a trapped atomic Bose condensate and an optomechanical end mirror mediated by a cavity field. Coupling between the mirror and the cold gas arises from the fact that the cavity field can produce density oscillations in the g...

A class of Hamiltonians that are experimentally feasible in several contexts within quantum optics and lead to so-called cooling by heating for fermionic as well as for bosonic systems has been analyzed numerically. We have found a large range of parameters for which cooling by heating can be observ...

We study the spontaneous excitation of a uniformly accelerated two-level atom nonlinearly coupled to vacuum Dirac field fluctuations using the formalism proposed by Dalibard, Dupont-Roc, and Cohen-Tannoudji and generalized by us to the present case in the current paper. We find that a cross term inv...

Measurement-induced back-action, a direct consequence of the Heisenberg uncertainty principle, is the defining feature of quantum measurements. We use quantum measurement theory to analyze the recent experiment of Safavi-Naeini et al. [ Phys. Rev. Lett. 108 033602 (2012)], and show that the results...

Fourth-order coherence determines the visibility of interference fringes observed in two-photon correlation measurements. In some cases, one photon triggers the presence of its conjugate twin in the interferometer. Therefore, spatial or spectral filtering of the trigger photon may change the visibil...

We theoretically investigate properties of individual bright spatial solitons and their interaction in nonlocal media with competing focusing and defocusing nonlinearities. We consider the general case with both nonlinear responses characterized by different strengths and degrees of nonlocality. We ...

The Jaynes-Cummings model without the rotating-wave approximation can be solved exactly by an extended Swain ansatz with conserved parity. Analytical approximations are then performed at different levels. The well-known rotating-wave approximation (RWA) is naturally covered in the present zeroth- an...

The nonlinear wave propagation and scattering processes in discrete optical heterostructures is studied both analytically and numerically. The presented theory describes the reflection and tunneling of lattice solitons at interfaces. In particular, the derived expressions allow us to construct the r...

In this Rapid Communication, we experimentally demonstrate that the signal velocity, defined as the earliest time when a signal is detected above the realistic noise floor, may be altered by a region of anomalous dispersion. We encode information in the spatial degree of freedom of an optical pulse ...

Wigner gave a well-known proof of Kramers degeneracy for time reversal invariant systems containing an odd number of half-integer spin particles. But Wigner's proof relies on the assumption that the Hamiltonian has an eigenvector, and thus does not apply to many quantum systems of physical interest....

A consensus that questions the perfunctory use of the quantum adiabatic theorem has emerged since Marzlin and Sanders [ Phys. Rev. Lett. 93 160408 (2004)] showed the existence of an inconsistency in the applicability of the theorem. Further analysis proved that the inconsistency may arise from the ...

We analyze the quantum Zeno dynamics that takes place when a field stored in a cavity undergoes frequent interactions with atoms. We show that repeated measurements or unitary operations performed on the atoms probing the field state confine the evolution to tailored subspaces of the total Hilbert s...

We relate the principle of quantum-memory-assisted entropic uncertainty to quantum teleportation and show geometrically that any two-qubit state which lowers the upper bound of this uncertainty relation is useful for teleportation. We also explore the efficiency of this entropic uncertainty principl...

We show that, in analogy to light fields, effective bosonic modes of atomic ensembles in the Holstein-Primakoff representation can be prepared in multimode squeezed states, and multipartite continuous-variable cluster and Greenberger-Horne-Zeilinger (GHZ) entangled states. Our scheme uses a cascade ...

It was recently shown that entanglement in quantum systems being in a nonequilibrium state can appear at much higher temperatures than in an equilibrium state. However, any system is subject to the natural relaxation process establishing equilibrium. The work deals with the numerical study of entang...

We propose a sequence of pulses intended to preserve the state of a qubit in the presence of strong, coherent coupling to another quantum system. The sequence can be understood as a generalized swap sequence and works in formal analogy to the well-known spin echo. Since the resulting effective decoh...

Inside computer networks, different information processing tasks are necessary to deliver the user data efficiently. This processing can also be done in the quantum domain. We present simple optical quantum networks where the orbital angular momentum (OAM) of a single photon is used as an ancillary ...

The effects of an electric field on the magnetically induced ⁶Li-⁴⁰K Feshbach resonances are investigated theoretically by using the asymptotic bound-state model. We calculate the positions and widths of the Feshbach resonances observed in the experiments in the presence of an electric field and giv...

Spin-polarized metastable atoms of ultracold ytterbium are trapped at high density and their inelastic collisional properties are measured. We reveal that in collisions of Yb(³ P₂) with Yb(¹ S₀) there is relatively weak inelastic loss, but with a significant spin dependence consistent with Zeeman su...

Long-range electrostatic, induction, and dispersion coefficients including terms of order R⁻⁸ have been calculated by the sum over states method using time-dependent density-functional theory. We also computed electrostatic moments and static polarizabilities of the individual diatoms up to the octo...

We present a theoretical analysis of single ionization of He by C⁶⁺ at an impact energy of 100 Mev/amu and a momentum transfer Q=0.75 a.u. Relativistic, second-order Born, and distorted-wave effects on fully differential cross sections are examined. It is demonstrated that neither of them is able to...

In recent attempts to control strong-field phenomena such as molecular dissociation, undesired ionization sometimes seriously limited the outcome. In this work we examine the capability of quantum optimal control theory to suppress the ionization by rational pulse shaping. Using a simple model syste...

We study small systems of strongly interacting ultracold atoms under the influence of gauge potentials and spin-orbit couplings. We use second-order perturbation theory in tunneling, derive an effective theory for the strongly correlated insulating states with one atom per site, and solve it exactly...

We study the generation of entanglement for interacting cold atoms in a three-site ring. The entanglement is generated by managing the interaction between two distinct atomic species. It is found that the current of one of the species can be used as a good indicator of entanglement generation. The t...

We develop a symmetry classification scheme to find ground states of pseudo-spin-1/2, spin-1, and spin-2 spin-orbit-coupled spinor Bose-Einstein condensates and show that as the SO(2) symmetry of simultaneous spin and space rotations is broken into discrete cyclic groups, various types of lattice st...