arXiv subjects

Bimalendu Deb

Publications and source records attributed to Bimalendu Deb.

At least 19 recordsLinked to original sources

arXiv2026

Enhanced quantum thermometry near a dissipative phase transition in a driven Kerr cavity

We investigate quantum thermometry in a driven--dissipative Kerr cavity coupled to a thermal reservoir. The system exhibits a finite-size precursor of a dissipative phase transition, characterized by a pronounced minimum of the Liouvillian gap and a sharp jump in the steady-state physical observables such as average photon number at the critical driving strength. We show that this regime leads to strong enhancement of the quantum Fisher information (QFI) for temperature estimation. Using an effective two-branch description, we show that the enhancement originates from temperature-induced redistribution of the weight factors in photon number distribution between low- and high-photon-number branches, which is described by an effective binary Fisher information. By optimizing the coherent drive, the enhanced response persists over an extended low-temperature, low-thermal-occupation regime and yields a favorable relative temperature-uncertainty bound. These results identify finite-size precursors of dissipative phase transitions in Kerr-cavity platforms as useful resources for tunable nonequilibrium quantum thermometry. We further show that the predicted thermometric enhancement is accessible in a parameter regime compatible with circuit quantum electrodynamics (circuit-QED) platforms.

quant-ph↗

arXiv2026

Ion-atom two-qubit quantum gate based on phonon blockade

We theoretically demonstrate the universal two-qubit CNOT gate between an ionic and an atomic qubit relying on Rydberg excitation of the atom and the resulting phonon blockade in the motional states of the harmonically trapped ion. The phonon blockade arises due to strong ion-atom interaction when the atom is excited to a Rydberg state. For realistic parameters, the gate fidelity is found to be about $90\%$. In a previous paper [S. Mudli {\it et al.} Phys. Rev. A 110, 062618 (2024)], it was shown that a trapped ion can mediate interaction between two largely separated Rydberg atoms, and this mediated interaction can be leveraged to perform a universal two-qubit gate operation between neutral atom qubits in optical tweezers. These demonstrations suggest that an ion-atom hybrid system can serve as a resourceful platform or module for quantum computing and quantum networking as it can utilize the best features of charged as well as neutral atom qubits. Finally, we discuss how to achieve higher gate fidelity by extending our proposed protocol and operating in a different parameter regime.

quant-ph↗

arXiv2026

Controlling correlations of a polaritonic Luttinger liquid by engineered cross-Kerr nonlinearity

We study correlation properties of polaritons at zero temperature in a multiconnected Jaynes--Cummings (MCJC) lattice on a superconducting circuit quantum electrodynamics platform with engineered cross-Kerr nonlinearity that mimics attractive nearest-neighbour interaction. A multi-connected Jaynes--Cummings lattice is a one-dimensional lattice constructed from alternating qubits and resonators with different left and right couplings. The nearest-neighbour interaction or cross-Kerr coupling is implemented dispersively through ladder-type qutrits between each nearest neighboring pair of resonator modes. Projecting onto the lower-polaritonic manifold, we derive an extended two-mode (bipartite) Bose--Hubbard-like model featuring on-site and attractive nearest-neighbor interactions. Employing a continuum bosonization approach, we express the Hamiltonian in terms of symmetric ($+$) and antisymmetric ($-$) collective modes. In the regime where the ($-$) sector acquires a finite gap, one can reduce the system to an effective single-component Luttinger liquid model for the $+$ sector. The cross-Kerr term reduces the compressibility of the ($+$) mode, thereby enhancing the corresponding Luttinger parameter $K_{+}$, resulting in the slower algebraic decay of single-particle correlations, $G(x)\propto|x|^{-1/(4K_{+})}$.

quant-ph↗

arXiv2026

Rydberg atom parity gate based on dark state resonances

Quantum computation (QC) and digital quantum simulation (DQS) essentially require two- or multi-qubit controlled-NOT or -phase gates. We propose an alternative pathway for QC and DQS using a three-qubit parity gate in a Rydberg atom array. The basic principle of the Rydberg atom parity gate (RPG) is that the operation on the target qubit is controlled by the parity of the control qubits. First, we discuss how to construct an RPG based on a dark state resonance. We optimize the gate parameters by numerically analyzing the time evolution of the computational basis states to maximize the gate fidelity. We also show that our proposed RPG is extremely robust against the Rydberg blockade error. To demonstrate the efficiency of the proposed RPG over the conventional CNOT or CZ gate in QC and DQS, we implement the Deutsch-Jozsa algorithm and simulate the Ising Hamiltonian. The results show that RPG can be a better substitute of the CNOT gate to yield better results, as it decreases the circuit noise by reducing circuit depth.

quant-ph↗

arXiv2025

Neutral-atom quantum computation using multi-qubit geometric gates via adiabatic passage

Adiabatic geometric phase gates offer enhanced robustness against fluctuations compared to con- ventional Rydberg blockade-based phase gates that rely on dynamical phase accumulation. We theoretically demonstrate two- and multi-qubit phase gates in a neutral atom architecture, relying on a double stimulated Raman adiabatic passage (double-STIRAP) pulse sequence that imprints a controllable geometric phase on the qubit systems. The system is designed in such a way that every atom is individually addressable, and moreover, no extra laser is required to be applied on the target atom while scaling up the system from two- to multi-qubit quantum gates. The gate fidelity has been numerically analyzed by changing the gate operation time, and we find that 98% to 99% fidelity can be achieved for gate time $\simeq$ 0.6 $\mu$s. We perform a systematic error analysis, which re- veals that our proposed gates can exhibit strong resilience against fluctuations in Rabi frequencies, finite blockade strength, and atomic position variations. These results establish our approach as a physically feasible and scalable pathway toward fault-tolerant quantum computation with neutral atoms. We simulate Grover's search algorithm for two-, three-, and four-qubit systems with high success probability and thereby demonstrate the utility and scalability of our proposed gates for quantum computation.

quant-ph↗

arXiv2025

Toffoli and C$^\text{n}$NOT (n$>2$) gates in a neutral-atom platform using Rydberg coupling and dark state resonances

We propose a protocol for realizing a Toffoli gate using neutral-atom qubits in optical tweezers. Two ground-state hyperfine levels of the atoms are considered as qubit states. Our method relies on the strong and long-range interactions between atoms due to Rydberg excitations and the occurrence of dark states in the target qubit, with both control and target qubits being individually addressed with laser pulses. Our gate protocol enables precise control over the quantum states of individual qubits, effectively suppressing undesirable transitions to ensure high-fidelity gate performance. The gate fidelity is estimated to be about $96\%$ for realistic system parameters. We further demonstrate a C$^\text{n}$NOT gate with $n >2$ by exploiting the Rydberg antiblockade mechanism, which allows multiple atoms within the blockade radius to be simultaneously excited to the Rydberg states. Thus, our approach may open a promising route to multi-qubit controlled operations for quantum computation.

quant-ph↗

arXiv2025

Dynamic structure factor of a driven-dissipative Bose-Hubbard model

Dynamic structure factor (DSF) is important for understanding excitations in many-body physics; it reveals information about the spectral and spatial correlations of fluctuations in quantum systems. Collective phenomena like quantum phase transitions of ultracold atoms are addressed by harnessing density fluctuations. Here, we calculate the DSF of a nonequilibrium spinless Bose-Hubbard model (BHM) from the perspective of dissipative phase transition (DPT) in a steady state. Our methodology uses a homogeneous mean-field approximation to make the single-site hierarchy simpler and applies the Lindbladian perturbation method (LPM) to go beyond the single site, limited by the ratio of the inter-site hopping term to the Liouvillian gap as a small parameter. Our results show that the DSF near a DPT point is characteristically different from that away from the transition point, providing a clear density spectral signature of the DPT. In addition to comparing the two numerical frameworks, the mean-field results serve as a benchmark for proof-of-principle robustness of LPM. Despite the numerical difficulty, our methodology provides a computationally accessible route for studying density fluctuations in an open lattice quantum system without requiring large-scale computation.

cond-mat.quant-gas↗

arXiv2024

Driven-dissipative fermionized topological phases of strongly interacting bosons

We study the optical response of a one-dimensional array of strongly nonlinear optical microcavities with alternating tunnel transmissivities, mimicking the paradigmatic Su-Schriefer Heeger model. We show that the non-equilibrium steady state of the bosonic system contains clear signatures of fermionization when the intra-cavity Kerr non-linearity is stronger than both losses and inter-site tunnel coupling. Furthermore, by changing the experimentally controllable parameters detuning and driving strength, in a topologically non-trivial phase, one can selectively excite either the bulk or edge modes or both modes, revealing interesting topological properties in a non-equilibrium system.

cond-mat.quant-gas↗

arXiv2024

Ion-mediated interaction and controlled phase gate operation between two atomic qubits

We propose a toy model of ion-atom hybrid quantum system for quantum computing. We show that when two atomic qubits in two largely separated optical tweezers interact with a single trapped ion through Rydberg excitation of the atoms, there exists an ion-mediated atom-atom interaction which exceeds the direct interatomic interaction at large separation. We employ this mediated interaction to demonstrate two-qubit control phase gate operation with 97\% fidelity by addressing the individual atomic qubits with lasers.

quant-ph↗

arXiv2024

Hyperradiance, photon blockade and concurrence in a pair of qubits inside a driven cavity

We theoretically study the radiance properties of a pair of qubits inside a single-mode cavity driven by a two-photon drive. Our results show that, when the two qubits are strongly coupled to the cavity field, the collective radiation emitted from the qubits exhibits hyperradiance which can be detected as a signature of two qubit entanglement in the weak-driving regime. We quantify the entanglement in terms of concurrence. Additionally, we study the radiance behaviour in the presence of an intracavity Kerr-nonlinear medium that leads to two-photon blockade. Our results suggest that this system with nonlinearity may act as a quadrature-squeezed and hyperradiant two-photon source.

physics.atom-ph↗

arXiv2023

Thermal effects in an imbalanced dipolar fermionic superfluid

We investigate the temperature effects in an imbalanced superfluid atomic Fermi gas. We consider a bilayer system of two-component dipolar fermionic atoms with one layer containing atoms of one component and the other layer the atoms of other component with an imbalance between the populations of the two components. This imbalance results in uniform and nonuniform superfluid phases such as phase-separated BCS, Fulde-Ferrel-Larkin-Ovchinnikov (FFLO), Sarma and normal Fermi liquid phases for different system parameters. Using the mean-field BCS theory together with the superfluid mass-density criterion we classify different phases in thermodynamic phase diagram. Our results indicate that for a dipolar Fermi system the Sarma phase is stable for large imbalance at finite temperature below the critical temperature, and the FFLO phase is stable for intermediate imbalance on the BCS side of a BCS-BCE crossover. The phase diagram in the temperature and population imbalance plane indicate three Lifshitz points: one corresponding to coexistance of BCS, FFLO and normal Fermi liquid phase while the other two correspond to the coexistance of the Sarma phase, FFLO phase and normal Fermi phase for dipolar interactions.

cond-mat.quant-gas↗

arXiv2023

Resonance fluorescence in $\Lambda$, $V$ and $\Xi$ -- type three-level configurations

We theoretically study the resonance fluorescence spectra of the lambda ($\Lambda$), vee ($V$) and cascade ($\Xi$) type three-level configurations. It is shown that each system with two detuning frequencies can be modelled using the $SU(3)$ symmetry group to derive a generalized optical Bloch equation. For each configuration, this equation is solved to calculate the two-time correlation function by invoking the quantum regression theorem. The incoherent part of the power spectra gives the characteristic multi-peak fluorescence profiles which are different for different configurations. We also discuss how the dressed-state structure of such system can explain the origin of quintuplet profile of the fluorescent spectrum.

quant-ph↗

arXiv2023

Trapped ion-mediated interactions between two distant trapped atoms

We theoretically show that when two largely separated trapped atoms interact with a trapped ion via Rydberg excitation of the atoms, the ion-mediated interaction between the atoms exceeds the direct atom-atom interaction by several orders of magnitude. Since the motion of the atoms is much slower than the motion of the ion, we resort to Born-Oppenheimer approximation to calculate the ion-mediated adiabatic potential. We also calculate the ion-mediated phonon modes of the atoms that are separated by more than 10 micron. For cylindrical geometry of the system and both the atoms being excited to the same Rydberg state, the stretched and center-of-mass (COM) axial or transverse phonon modes are found to be almost degenerate, while the phonon modes are non-degenerate when one atom is in a Rydberg state and the other in the ground state. We discuss the non-adiabatic effects in the system that give rise to a Gauge structure and associated geometric phase in the system. This study may open a new perspective in quantum computing and exploring molecular physics associated with a conical intersection using an ion-atom hybrid architecture.

quant-ph↗

arXiv2022

Phase diffusion and fluctuations in a dissipative Bose-Josephson junction

We analyze the phase diffusion, quantum fluctuations and their spectral features of an one-dimensional Bose-Josephson junction (BJJ) coupled to a bosonic heat bath. We show the dependence of the phase diffusion coefficient on the on-site interaction parameter $U$ and the temperature in zero-phase and $\pi$-phase modes. We find that in the $\pi$-phase mode, the phase diffusion co-efficient as a function of $U$ decreases so long as $U$ is below a critical value while it increases above the critical value. This criticality of on-site interaction reflects a transition between Josephson oscillation and macroscopic quantum self-trapping (MQST) regime. Based on the thermal canonical Wigner distribution, we calculate the coherence factor to understand its dependence on temperature and on-site interaction energy in Josephson oscillation and MQST regime. Furthermore, we discuss coherent and incoherent spectral properties in connection with the fluctuations of the relative phase and the population imbalance in both zero and $\pi$-phase modes from weak to strong dissipation regime.

physics.atom-ph↗

arXiv2022

Electronic structure, spectroscopy, cold ion-atom elastic collision properties and photoassociation formation prediction of (MgCs)$^+$ molecular ion

Studies on the interactions between an alkali atom and an alkaline earth ion at low energy are important in the field of cold chemistry. In this paper we, extensively, study the structure, interactions, and dynamics of (MgCs)$^+$ molecular ion. We use an ab initio approach based on the formalism of non-empirical pseudo-potential for Mg$^{2+}$ and Cs$^+$ cores, large Gaussian basis sets and full valence configuration interaction. In this context, the (MgCs)$^+$ cation is treated as an effective two-electron system. Potential energy curves and their spectroscopic constants for the ground and the first 41 excited states of $^{1,3}\Sigma^+$, $^{1,3}\Pi$ and $^{1,3}\Delta$ symmetries are determined. Furthermore, we identify the avoided crossings between the electronic states of $^{1,3}\Sigma^+$ and $^{1,3}\Pi$ symmetries. These crossings are related to the charge transfer process between the two ionic limits Mg/Cs$^+$ and Mg$^+$/Cs. In addition, vibrational-level spacings, the transition and permanent dipole moments are presented and analysed. Using the produced potential energy data, the ground-state scattering wave functions and elastic cross sections for a wide range of energies are performed. Furthermore, we predict the formation of translationally and rotationally cold molecular ion (MgCs) + in the ground state electronic potential energy by stimulated Raman type process aided by ion-atom cold collision. In the low energy limit (< 1 mK), elastic scattering cross sections exhibit Wigner law threshold behaviour; while in the high energy limit the cross sections as a function of energy E go as E$^{-1/3}$. A qualitative discussion about the possibilities of forming the cold (MgCs)$^+$ molecular ions by photoassociative spectroscopy is presented.

physics.atom-ph↗

arXiv2022

Zero-threshold correlated-photon laser with a single trapped atom in a bimodal cavity

We demonstrate theoretically the feasibility of correlated entangled photon-pair generation with vanishing threshold in a bimodal cavity setup that uses a single V-type three level atom pumped by dual incoherent sources and driven by two coherent fields. The photon-pair is shown to be entangled only for low levels of the incoherent pumps and owes its origin solely to the coherent drives. Our results show that the dual incoherent pumping with no coherent drive can lead to amplification of the cavity fields with strong inter-mode antibunching but no entanglement. Though only coherent drives with no incoherent pumping can produce entangled photon-pairs, the entangled cavity fields can not be amplified beyond a certain limit using only coherent drives. However, the use of even small incoherent pumping in the presence of the coherent drives can amplify the generated entangled photon-pairs significantly. We analyse our results in terms of an interplay between coherent and incoherent processes involving cavity-dressed states. Both the inter- and intra-mode HBT functions exhibit temporal oscillations in the strong-coupling cavity QED regime. Our theoretical scheme for the generation of nonclassical and entangled photon pairs may find interesting applications in quantum metrology and quantum information science.

quant-ph↗

arXiv2021

A model study on superfluidity of a unitary Fermi gas of atoms interacting with a finite-ranged potential

We calculate Bardeen-Cooper-Schrieffer (BCS) state of a unitary Fermi gas of atoms interacting with the finite-ranged Jost-Kohn potential which has been recently shown to account for the resonant interactions [2019 {\rm J. Phys. B: At. Mol. Opt. Phys.} {\bf 52}, 165004]. Using exact scattering solution of the potential, we derive two-body ${\mathbf T}$-matrix element which is employed to construct the BCS Hamiltonian in momentum space. We present results on the energy- and range-dependence of the pairing gap and superfluid density and the range-dependence of the chemical potential for a wide variation of the scattering length including the unitary regime. In the zero range limit our calculated gap at the Fermi energy is found to be nearly equal to that calculated in mean-field theory with contact potential. The mean gap averaged over the full width at half maximum of the gap function in the zero range and unitary limits is found to be $0.42 E_F$ which is quite close to the recent result of the quantum Monte Carlo simulation [2018 {\rm Phys. Rev.A} {\bf 97}, 013601]. The chemical potential in the zero range limit also agrees well with that for the contact potential.

cond-mat.quant-gas↗

arXiv2021

Matter-wave phase operators for quantum atom optics: On the possibility of experimental verification

In early 90's Mandel and coworkers performed an experiment \cite{mandel} to examine the significance of quantum phase operators by measuring the phase between two optical fields. We show that this type of quantum mechanical phase measurement is possible for matter-waves of ultracold atoms in a double well. In the limit of low number of atoms quantum and classical phases are drastically different. However, in the large particle number limit, they are quite similar. We assert that the matter-wave counterpart of the experiment \cite{mandel} is realizable with the evolving technology of atom optics.

quant-ph↗