arXiv subjects

David Petrosyan

Publications and source records attributed to David Petrosyan.

At least 55 records · Page 3Linked to original sources

arXiv2012

Spatial correlations of Rydberg excitations in optically driven atomic ensembles

We study the emergence of many-body correlations in the stationary state of continuously-driven, strongly-interacting dissipative system. Specifically, we examine resonant optical excitations of Rydberg states of atoms interacting via long-range dipole-dipole and van der Waals potentials employing exact numerical solutions of the density matrix equations and Monte-Carlo simulations. Collection of atoms within a blockade distance form a "superatom" that can accommodate at most one Rydberg excitation. The superatom excitation probability saturates to 1/2 for coherently driven atoms, but is significantly higher for incoherent driving, approaching unity as the number of atoms increases. In the steady state of uniformly-driven, extended one-dimensional system, the saturation of superatoms leads to quasi-crystallization of Rydberg excitations whose correlations exhibit damped spatial oscillations. The behavior of the system under the van der Waals interaction potential can be approximated by an analytically soluble model based on a "hard-rod" interatomic potential.

physics.atom-ph↗

arXiv2012

Steady-state crystallization of Rydberg excitations in an optically driven lattice gas

We study resonant optical excitations of atoms in a one-dimensional lattice to the Rydberg states interacting via the van der Waals potential which suppresses simultaneous excitation of neighboring atoms. Considering two- and three-level excitation schemes, we analyze the dynamics and stationary state of the continuously-driven, dissipative many-body system employing time-dependent density-matrix renormalization group (t-DMRG) simulations. We show that two-level atoms can exhibit only nearest neighbor correlations, while three-level atoms under dark-state resonant driving can develop finite-range crystalline order of Rydberg excitations. We present an approximate rate equation model whose analytic solution yields qualitative understanding of the numerical results.

quant-ph↗

arXiv2012

Optimizing inhomogeneous spin ensembles for quantum memory

We propose a general method to maximize the fidelity of writing, storage and reading of quantum information (QI) in a spectrally inhomogeneous spin ensemble used as quantum memory. The method is based on preselecting the optimal spectral portion of the ensemble by a judiciously designed pulse. It allows drastic improvement of quantum memory realized by spin ensembles that store QI from a resonator or an optical beam.

quant-ph↗

arXiv2011

Dynamics and evaporation of defects in Mott-insulating clusters of boson pairs

Repulsively bound pairs of particles in a lattice governed by the Bose-Hubbard model can form stable incompressible clusters of dimers corresponding to finite-size n=2 Mott insulators. Here we study the dynamics of hole defects in such clusters corresponding to unpaired particles which can resonantly tunnel out of the cluster into the lattice vacuum. Due to bosonic statistics, the unpaired particles have different effective mass inside and outside the cluster, and "evaporation" of hole defects from the cluster boundaries is possible only when their quasi-momenta are within a certain transmission range. We show that quasi-thermalization of hole defects occurs in the presence of catalyzing particle defects which thereby purify the Mott insulating clusters. We study the dynamics of one-dimensional system using analytical techniques and numerically exact t-DMRG simulations. We derive an effective strong-interaction model that enables simulations of the system dynamics for much longer times. We also discuss a more general case of two bosonic species which reduces to the fermionic Hubbard model in the strong interaction limit.

quant-ph↗

arXiv2011

Electromagnetically induced transparency with Rydberg atoms

We present a theory of electromagnetically induced transparency in a cold ensemble of strongly interacting Rydberg atoms. Long-range interactions between the atoms constrain the medium to behave as a collection of superatoms, each comprising a blockade volume that can accommodate at most one Rydberg excitation. The propagation of a probe field is affected by its two-photon correlations within the blockade distance, which are strongly damped due to low saturation threshold of the superatoms. Our model is computationally very efficient and is in quantitative agreement with the results of recent experiment of Pritchard et al. [Phys. Rev. Lett. 105, 193603 (2010)].

quant-ph↗

arXiv2010

Strongly interacting photons in hollow-core waveguides

Hollow-core photonic-crystal waveguides filled with cold atoms can support giant optical nonlinearities through nondispersive propagation of light tightly confined in the transverse direction. Here we explore electromagnetically induced transparency is such structures, considering a pair of counter-propagating weak quantum fields in the medium of coherently driven atoms in the ladder configuration. Strong dipole--dipole interactions between optically excited, polarized Rydberg states of the atoms translate into a large dispersive interaction between the two fields. This can be used to attain a spatially-homogeneous conditional phase shift of pi for two single-photon pulses, realizing a deterministic photonic phase gate, or to implement a quantum nondemolition measurement of the photon number in the signal pulse by a coherent probe, thereby achieving a heralded source of single or few photon pulses.

quant-ph↗

arXiv2010

Atom number filter in an optical lattice

We present an efficient procedure to filter out from an optical lattice, having inhomogeneous site occupation number, only preselected number of bosonic atoms per site and place them into another internal atomic state, creating thereby a lattice with desired site occupation number.

cond-mat.quant-gas↗

arXiv2010

Exotic few-body bound states in a lattice

Strongly-interacting ultra-cold atoms in tight-binding optical lattice potentials provide an ideal platform to realize the fundamental Hubbard model. Here, after outlining the elementary single particle solution, we review and expand our recent work on complete characterization of the bound and scattering states of two and three bosonic atoms in a one-dimensional optical lattice. In the case of two atoms, there is a family of interaction-bound "dimer" states of co-localized particles that exists invariantly for either attractive or repulsive on-site interaction, with the energy below or above the two-particle scattering continuum, respectively. Adding then the third particle -- "monomer" -- we find that, apart from the simple strongly-bound "trimer" corresponding to all three particles occupying the same lattice site, there are two peculiar families of weakly-bound trimers with energies below and above the monomer-dimer scattering continuum, the corresponding binding mechanism being an effective particle exchange interaction.

cond-mat.quant-gas↗

arXiv2010

State transfer in static and dynamic spin chains with disorder

We examine the speed and fidelity of several protocols for state or single excitation transfer in finite spin chains subject to diagonal and off-diagonal disorder. We find that, for a given chain length and maximal achievable inter-spin exchange (XY) coupling strength, the optimal static spin-coupling protocol, implementing the fastest state transfer between the two ends of the chain, is more susceptible to off-diagonal (XY coupling) disorder, as compared to a much slower but robust adiabatic transfer protocol with time-dependent coupling strengths.

quant-ph↗

arXiv2009

Three-body bound states in a lattice

We pursue three-body bound states in a one-dimensional tight-binding lattice described by the Bose-Hubbard model with strong on-site interaction. Apart from the simple strongly-bound "trimer" state corresponding to all three particles occupying the same lattice site, we find two novel kinds of weakly-bound trimers with energies below and above the continuum of scattering states of a single particle ("monomer") and a bound particle pair ("dimer"). The corresponding binding mechanism can be inferred from an effective Hamiltonian in the strong-coupling regime which contains an exchange interaction between the monomer and dimer. In the limit of very strong on-site interaction, the exchange-bound trimers attain a universal value of the binding energy. These phenomena can be observed with cold atoms in optical lattices.

cond-mat.other↗

arXiv2009

Scattering resonances and two-particle bound states of the extended Hubbard model

We present a complete derivation of two-particle states of the one-dimensional extended Hubbard model involving attractive or repulsive on-site and nearest-neighbour interactions. We find that this system possesses scattering resonances and two families of energy-dependent interaction-bound states which are not present in the Hubbard model with the on-site interaction alone.

quant-ph↗

arXiv2009

Attractively bound pairs of atoms in the Bose-Hubbard model and antiferromagnetism

We consider a periodic lattice loaded with pairs of bosonic atoms tightly bound to each other via strong attractive on-site interaction that exceeds the inter-site tunneling rate. An ensemble of such lattice-dimers is accurately described by an effective Hamiltonian of hard core bosons with strong nearest-neighbor repulsion which is equivalent to the $XXZ$ model with Ising-like anisotropy. We calculate the ground-state phase diagram for a one-dimensional system which exhibits incompressible phases, corresponding to an empty and a fully filled lattice (ferromagnetic phases) and a half-filled alternating density crystal (anti-ferromagnetic phase), separated from each other by compressible phases. In a finite lattice the compressible phases show characteristic oscillatory modulations on top of the anti-ferromagnetic density profile and in density-density correlations. We derive a kink model which provides simple quantitative explanation of these features. To describe the long-range correlations of the system we employ the Luttinger liquid theory with the relevant Luttinger parameter $K$ obtained exactly using the Bethe Ansatz solution. We calculate the density-density as well as first-order correlations and find excellent agreement with numerical results obtained with density matrix renormalization group (DMRG) methods. We also present a perturbative treatment of the system in higher dimensions.

cond-mat.stat-mech↗

arXiv2008

Two-particle states in the Hubbard model

We consider a pair of bosonic particles in a one-dimensional tight-binding periodic potential described by the Hubbard model with attractive or repulsive on-site interaction. We derive explicit analytic expressions for the two-particle states, which can be classified as (i) scattering states of asymptotically free particles and (ii) interaction-bound dimer states. Our results provide a very transparent framework to understand the properties of interacting pairs of particles in a lattice.

quant-ph↗

arXiv2008

Quantum liquid of repulsively bound pairs of particles in a lattice

Repulsively interacting particles in a periodic potential can form bound composite objects, whose dissociation is suppressed by a band gap. Nearly pure samples of such repulsively bound pairs of cold atoms -- "dimers" -- have recently been prepared by Winkler et al. [Nature 441, 853 (2006)]. We here derive an effective Hamiltonian for a lattice loaded with dimers only and discuss its implications to the many-body dynamics of the system. We find that the dimer-dimer interaction includes strong on-site repulsion and nearest-neighbor attraction which always dominates over the dimer kinetic energy at low temperatures. The dimers then form incompressible, minimal-surface "droplets" of a quantum lattice liquid. For low lattice filling, the effective Hamiltonian can be mapped onto the spin-1/2 XXZ model with fixed total magnetization which exhibits a first-order phase transition from the "droplet" to a "gas" phase. This opens the door to studying first order phase transitions using highly controllable ultracold atoms.

cond-mat.other↗

arXiv2008

Quantum dynamics of one and two bosonic atoms in a combined tight-binding periodic and weak parabolic potential

Strongly interacting bosonic particles in a tight-binding periodic potential superimposed by a weak parabolic trap is a paradigm for many cold atom experiments. Here, after revisiting the single particle problem, we study interaction-bound dimers of bosonic atoms in the combined lattice and parabolic potential. We consider both repulsively- and attractively-bound dimers and find pronounced differences in their behaviour. We identify conditions under which attractive and repulsive dimers exhibit analogous dynamics. Our studies reveal that coherent transport and periodic oscillations of appropriately prepared one- and two-atom wavepackets can be achieved, which may facilitate information transfer in optical lattice based quantum computation schemes.

quant-ph↗

arXiv2008

Quantum information processing with single photons and atomic ensembles in microwave coplanar waveguide resonators

We show that pairs of atoms optically excited to the Rydberg states can strongly interact with each other via effective long-range dipole-dipole or van der Waals interactions mediated by their non-resonant coupling to a common microwave field mode of a superconducting coplanar waveguide cavity. These cavity mediated interactions can be employed to generate single photons and to realize in a scalable configuration a universal phase gate between pairs of single photon pulses propagating or stored in atomic ensembles in the regime of electromagnetically induced transparency.

quant-ph↗

arXiv2007

Tunable photonic band gaps with coherently driven atoms in optical lattices

Optical lattice loaded with cold atoms can exhibit a tunable photonic band gap for a weak probe field under the conditions of electromagnetically induced transparency. This system possesses a number of advantageous properties, including reduced relaxation of Raman coherence and the associated probe absorption, and simultaneous enhancement of the index modulation and the resulting reflectivity of the medium. This flexible system has a potential to serve as a testbed of various designs for the linear and nonlinear photonic band gap materials at a very low light level and can be employed for realizing deterministic entanglement between weak quantum fields.

quant-ph↗

arXiv2007

Coherent population transfer in a chain of tunnel coupled quantum dots

We consider the dynamics of a single electron in a chain of tunnel coupled quantum dots, exploring the formal analogies of this system with some of the laser-driven multilevel atomic or molecular systems studied by Bruce W. Shore and collaborators over the last 30 years. In particular, we describe two regimes for achieving complete coherent transfer of population in such a multistate system. In the first regime, by carefully arranging the coupling strengths, the flow of population between the states of the system can be made periodic in time. In the second regime, by employing a "counterintuitive" sequence of couplings, the coherent population trapping eigenstate of the system can be rotated from the initial to the final desired state, which is an equivalent of the STIRAP technique for atoms or molecules. Our results may be useful in future quantum computation schemes.

quant-ph↗