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Mikhail A. Baranov

Publications and source records attributed to Mikhail A. Baranov.

15 recordsLinked to original sources
arXiv2026

Reduced density matrix and entanglement Hamiltonian for a free real scalar field on an interval

An exact result for the reduced density matrix on a finite interval for a $1+1$ dimensional free real scalar field in the ground state is presented. In the massless case, the Williamson decomposition of the appearing kernels is explicitly performed, which allows to reproduce the known result for the entanglement (modular) Hamiltonian and, for a small mass $M$ of the field, find the leading $\sim1/\ln M$ non-local corrections. In the opposite $M\to\infty$ case, it is argued that, up to terms $O(M^{-1/2})$, the entanglement Hamiltonian is local with the density being the Hamiltonian density spatially modulated by a triangular-shape function.

quant-ph↗
arXiv2022

Topological phonons in arrays of ultracold dipolar particles

The notion of topology in physical systems is associated with the existence of a nonlocal ordering that is insensitive to a large class of perturbations. This brings robustness to the behaviour of the system and can serve as a ground for developing new fault-tolerant applications. We discuss how to design and study a large variety of topology-related phenomena for phonon-like collective modes in arrays of ultracold polarized dipolar particles. These modes are coherently propagating vibrational excitations, corresponding to oscillations of particles around their equilibrium positions, which exist in the regime where long-range interactions dominate over single-particle motion. We demonstrate that such systems offer a distinct and versatile tool to investigate a wide range of topological effects in a single experimental setup with a chosen underlying crystal structure by simply controlling the anisotropy of the interactions via the orientation of the external polarizing field. Our results show that arrays of dipolar particles provide a promising unifying platform to investigate topological phenomena with phononic modes.

cond-mat.quant-gas↗
arXiv2020

Monitoring Quantum Simulators via Quantum Non-Demolition Couplings to Atomic Clock Qubits

We discuss monitoring the time evolution of an analog quantum simulator via a quantum non-demolition (QND) coupling to an auxiliary `clock' qubit. The QND variable of interest is the `energy' of the quantum many-body system, represented by the Hamiltonian of the quantum simulator. We describe a physical implementation of the underlying QND Hamiltonian for Rydberg atoms trapped in tweezer arrays using laser dressing schemes for a broad class of spin models. As an application, we discuss a quantum protocol for measuring the spectral form factor of quantum many-body systems, where the aim is to identify signatures of ergodic vs. non-ergodic dynamics, which we illustrate for disordered 1D Heisenberg and Floquet spin models on Rydberg platforms. Our results also provide the physical ingredients for running quantum phase estimation protocols for measurement of energies, and preparation of energy eigenstates for a specified spectral resolution on an analog quantum simulator.

quant-ph↗
arXiv2020

Quantum Many-Body Physics with Ultracold Polar Molecules: Nanostructured Potential Barriers and Interactions

We design dipolar quantum many-body Hamiltonians that will facilitate the realization of exotic quantum phases under current experimental conditions achieved for polar molecules. The main idea is to modulate both single-body potential barriers and two-body dipolar interactions on a spatial scale of tens of nanometers to strongly enhance energy scales and, therefore, relax temperature requirements for observing new quantum phases of engineered many-body systems. We consider and compare two approaches. In the first, nanoscale barriers are generated with standing wave optical light fields exploiting optical nonlinearities. In the second, static electric field gradients in combination with microwave dressing are used to write nanostructured spatial patterns on the induced electric dipole moments, and thus dipolar interactions. We study the formation of inter-layer and interface bound states of molecules in these configurations, and provide detailed estimates for binding energies and expected losses for present experimental setups.

cond-mat.quant-gas↗
arXiv2019

Broadband plasmonic nanoparticles: fabrication, optical properties, and implications in liquid light chemiluminescence enhancement

Chemiphores are entities, which exhibit wide-band light emission without any external light source but just due to the chemical reaction resulting in the chemiluminescence effect. Since the chemiphores usually have low quantum efficiency, chemiluminescence is a weak optical effect. We found that plasmonic nanoparticles can efficiently enhance the peculiar effect of chemiluminescence due to the acceleration of the radiative decay of the chemiphore excited state which, in turn, enlarges the chemiluminescence yield. Correspondingly, plasmonic nanoparticles are nanoparticles with sub-wavelength sizes experiencing the absorption band in specific wavelength which are characterized by unique optical properties, as well as high localization of electromagnetic radiation. However, the broadband properties of plasmonic nanoparticles and their implications in liquid light, the chemiluminescence effect, is overlooked. Therefore, they can attract attention as novel materials for photonics, sensing, and forensic science. Here, fabrication techniques of broadband plasmonic nanoparticles are reported, and their interesting optical properties together with their applications in chemiluminescence effect are discussed, as well. We fabricated the nanoparticles with laser ablation in liquids (LAL) technique and propose the physical vapor deposition (PVD) synthesis with annealing-assisted treatment for further studies. Both techniques are accessible and allow production of ensembles of nanoparticles having shape and size distributions to exhibit broad plasmonic resonance which fit the wide-band emission of a chemiphore. Our results, in particular, a specific design for plasmonic nanoparticles placed on the dielectric material, lead the way toward a new generation of chemiluminescence-based devices starting from sensing, healthcare, biomedical research and quantum systems such as pump-free laser sources.

physics.optics↗
arXiv2018

Quantum Scanning Microscope for Cold Atoms

We present a detailed theoretical description of an atomic scanning microscope in a cavity QED setup proposed in Phys. Rev. Lett. 120, 133601 (2018). The microscope continuously observes atomic densities with optical subwavelength resolution in a nondestructive way. The super-resolution is achieved by engineering an internal atomic dark state with a sharp spatial variation of population of a ground level dispersively coupled to the cavity field. Thus, the atomic position encoded in the internal state is revealed as a phase shift of the light reflected from the cavity in a homodyne experiment. Our theoretical description of the microscope operation is based on the stochastic master equation describing the conditional time evolution of the atomic system under continuous observation as a competition between dynamics induced by the Hamiltonian of the system, decoherence effects due to atomic spontaneous decay, and the measurement backaction. Within our approach we relate the observed homodyne current with a local atomic density, and discuss the emergence of a quantum nondemolition measurement regime allowing continuous observation of spatial densities of quantum motional eigenstates without measurement backaction in a single experimental run.

quant-ph↗
arXiv2017

Dark state optical lattice with sub-wavelength spatial structure

We report on the experimental realization of a conservative optical lattice for cold atoms with sub-wavelength spatial structure. The potential is based on the nonlinear optical response of three-level atoms in laser-dressed dark states, which is not constrained by the diffraction limit of the light generating the potential. The lattice consists of a 1D array of ultra-narrow barriers with widths less than 10~nm, well below the wavelength of the lattice light, physically realizing a Kronig-Penney potential. We study the band structure and dissipation of this lattice, and find good agreement with theoretical predictions. The observed lifetimes of atoms trapped in the lattice are as long as 60 ms, nearly $10^5$ times the excited state lifetime, and could be further improved with more laser intensity. The potential is readily generalizable to higher dimension and different geometries, allowing, for example, nearly perfect box traps, narrow tunnel junctions for atomtronics applications, and dynamically generated lattices with sub-wavelength spacings.

cond-mat.quant-gas↗
arXiv2017

Adiabatic state preparation of stripe phases with strongly magnetic atoms

We propose a protocol for realizing the stripe phase in two spin models on a two-dimensional square lattice, which can be implemented with strongly magnetic atoms (Cr, Dy, Er, etc.) in optical lattices by encoding spin states into Zeeman sublevels of the ground state manifold. The protocol is tested with cluster-mean-field time-dependent variational ansätze, validated by comparison with exact results for small systems, which enable us to simulate the dynamics of systems with up to 64 sites during the state-preparation protocol. This allows, in particular, to estimate the time required for preparation of the stripe phase with high fidelity under real experimental conditions.

cond-mat.quant-gas↗
arXiv2015

Effects of Gapless Bosonic Fluctuations on Majorana Fermions in Atomic Wire Coupled to a Molecular Reservoir

We discuss the effects of quantum and thermal fluctuations on the Majorana edge states in a topological atomic wire coupled to a superfluid molecular gas with gapless excitations. We find that the coupling between the Majorana edge states remains exponentially decaying with the length of the wire, even at finite temperatures smaller than the energy gap for bulk excitations in the wire. This exponential dependence is controlled solely by the localization length of the Majorana states. The fluctuations, on the other hand, provide the dominant contribution to the preexponential factor, which increases with temperature and the length of the wire. More important is that thermal fluctuations give rise to a decay of an initial correlation between Majorana edge states to its stationary value after some thermalization time. This stationary value is sensitive to the temperature and to the length of the wire, and, although vanishing in the thermodynamic limit, can still be feasible in a mesoscopic system at sufficiently low temperatures. The thermalization time, on the other hand, is found to be much larger than the typical time scales in the wire, and is sufficient for quantum operations with Majorana fermions before the temperature-induced decoherence sets in.

cond-mat.quant-gas↗
arXiv2015

Majoranas in Noisy Kitaev Wires

Robustness of edge states and non-Abelian excitations of topological states of matter promises quantum memory and quantum processing, which is naturally immune against microscopic imperfections such as static disorder. However, topological properties will not in general protect quantum system from time-dependent disorder or noise. Here we take the example of a network of Kitaev wires with Majorana edge modes storing qubits to investigate the effects of classical noise in the crossover from the quasi-static to the fast fluctuation regime. We present detailed results for the Majorana edge correlations, and fidelity of braiding operations for both global and local noise sources preserving parity symmetry, such as random chemical potentials and phase fluctuations. While in general noise will induce heating and dephasing, we identify examples of long-lived quantum correlations in presence of fast noise due to motional narrowing, where external noise drives the system rapidly between the topological and non-topological phases.

quant-ph↗
arXiv2013

Probing Atomic Majorana Fermions in Optical Lattices

We introduce a one-dimensional system of fermionic atoms in an optical lattice whose phase diagram includes topological states of different symmetry classes. These states can be identified by their zero-energy edge modes which are Majorana fermions. We propose several universal methods of detecting the Majorana edge states, based on their genuine features: zero-energy, localized character of the wave functions, and induced non-local fermionic correlations.

cond-mat.quant-gas↗
arXiv2013

Majorana edge states in two atomic wires coupled by pair-hopping

We present evidence for the existence of Majorana edge states in a number conserving theory describing a system of spinless fermions on two wires that are coupled by a pair hopping. Our analysis is based on the combination of a qualitative low energy approach and numerical techniques using the Density Matrix Renormalization Group. We also discuss an experimental realization of pair-hopping interactions in cold atom gases confined in optical lattices, and its possible alternative applications to quantum simulation.

cond-mat.quant-gas↗
arXiv2010

Universal rates for reactive ultracold polar molecules in reduced dimensions

Analytic expressions describe universal elastic and reactive rates of quasi-two-dimensional and quasi-one-dimensional collisions of highly reactive ultracold molecules interacting by a van der Waals potential. Exact and approximate calculations for the example species of KRb show that stability and evaporative cooling can be realized for spin-polarized fermions at moderate dipole and trapping strength, whereas bosons or unlike fermions require significantly higher dipole or trapping strengths.

physics.atom-ph↗
arXiv2003

Mean-field Phase Diagram of Two-Dimensional Electrons with Disorder in a Weak Magnetic Field

We study two-dimensional interacting electrons in a weak perpendicular magnetic field with the filling factor $ν\gg 1$ and in the presence of a quenched disorder. In the framework of the Hartree-Fock approximation, we obtain the mean-field phase diagram for the partially filled highest Landau level. We find that the CDW state can exist if the Landau level broadening $1/2τ$ does not exceed the critical value $1/2τ_{c}=0.038ω_{H}$. Our analysis of weak crystallization corrections to the mean-field results shows that these corrections are of the order of $(1/ν)^{2/3}\ll 1$ and therefore can be neglected.

cond-mat.mes-hall↗