Publications
39 results found
Zens M, Krimer DO, Dhar HS, et al., 2021, Periodic Cavity State Revivals from Atomic Frequency Combs, PHYSICAL REVIEW LETTERS, Vol: 127, ISSN: 0031-9007
Dhar HS, Zuo Z, Rodrigues JD, et al., 2021, Quest for vortices in photon condensates, PHYSICAL REVIEW A, Vol: 104, ISSN: 2469-9926
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- Citations: 1
Nyman RA, Dhar HS, Rodrigues JD, et al., 2021, Phase transitions of light in a dye-filled microcavity: observations and simulations, Journal of Physics: Conference Series, Vol: 1919, Pages: 012006-012006, ISSN: 1742-6588
<jats:title>Abstract</jats:title> <jats:p>Photon thermalisation and condensation in dye-filled microcavities is a growing area of scientific interest, at the intersection of photonics, quantum optics and statistical physics. We give here a short introduction to the topic, together with an explanation of some of our more important recent results. A key result across several projects is that we have a model based on a detailed physical description which has been used to accurately describe experimental observations. We present a new open-source package in Python called PyPBEC which implements this model. The aim is to enable the reader to readily simulate and explore the physics of photon condensates themselves, so this article also includes a working example code which can be downloaded from the GitHub repository.</jats:p>
Rodrigues JD, Dhar HS, Walker BT, et al., 2021, Learning the Fuzzy Phases of Small Photonic Condensates, PHYSICAL REVIEW LETTERS, Vol: 126, ISSN: 0031-9007
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- Citations: 4
Dhar HS, Rodrigues JD, Walker BT, et al., 2020, Transport and localization of light inside a dye-filled microcavity, Physical Review A: Atomic, Molecular and Optical Physics, Vol: 102, Pages: 1-9, ISSN: 1050-2947
The driven-dissipative nature of light-matter interaction inside a multimode, dye-filled microcavity makes it an ideal system to study nonequilibrium phenomena, such as transport. In this work, we investigate how light is efficiently transported inside such a microcavity, mediated by incoherent absorption and emission processes. In particular, we show that there exist two distinct regimes of transport, viz. conductive and localized, arising from the complex interplay between the thermalizing effect of the dye molecules and the nonequilibrium influence of driving and loss. The propagation of light in the conductive regime occurs when several localized cavity modes undergo dynamical phase transitions to a condensed, or lasing, state. Furthermore, we observe that, while such transport is robust for weak disorder in the cavity potential, strong disorder can lead to localization of light even under good thermalizing conditions. Importantly, the exhibited transport and localization of light is a manifestation of the nonequilibrium dynamics rather than any coherent interference in the system.
Marques Rodrigues J, Walker BT, Dhar HS, et al., 2020, Non-stationary statistics and formation jitter in transient photon condensation, Nature Communications, Vol: 11, ISSN: 2041-1723
While equilibrium phase transitions are easily described by order parameters and free-energylandscapes, for their non-stationary counterparts these quantities are usually ill-defined. Here,we probe transient non-equilibrium dynamics of an optically pumped, dye-filled microcavity. Wequench the system to a far-from-equilibrium state and find delayed condensation close to a criticalexcitation energy, a transient equivalent of critical slowing down. Besides number fluctuations nearthe critical excitation energy, we show that transient phase transitions exhibit timing jitter in thecondensate formation. This jitter is a manifestation of the randomness associated with spontaneousemission, showing that condensation is a stochastic, rather than deterministic process. Despite thenon-equilibrium character of this phase transition, we construct an effective free-energy landscapethat describes the formation jitter and allows, in principle, its generalization to a wider class ofprocesses.
Walker BT, Rodrigues JD, Dhar HS, et al., 2020, Non-stationary statistics and formation jitter in transient photon condensation, Publisher: NATURE PUBLISHING GROUP
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- Citations: 9
Walker BT, Hesten HJ, Dhar HS, et al., 2019, Non-critical slowing down of photonic condensation, Physical Review Letters, Vol: 123, ISSN: 0031-9007
We investigate the response of a photonic gas interacting with a reservoir ofpumped dye-molecules to quenches in the pump power. In addition to the expecteddramatic critical slowing down of the equilibration time around phasetransitions we find extremely slow equilibration even far away from phasetransitions. This non-critical slowing down can be accounted for quantitativelyby fierce competition among cavity modes for access to the molecularenvironment, and we provide a quantitative explanation for this non-criticalslowing down.
Singha Roy S, Dhar HS, 2019, Effect of long-range interactions on multipartite entanglement in Heisenberg chains, PHYSICAL REVIEW A, Vol: 99, Pages: 062318-1-062318-8, ISSN: 2469-9926
It is well known that the notions of spatial locality are often lost in quantum systems with long-range interactions, as exhibited by the emergence of phases with exotic long-range order and faster propagation of quantum correlations. We demonstrate here that such induced “quasinonlocal” effects do not necessarily translate to growth of global entanglement in the quantum system. By investigating the ground and quenched states of the variable-range, spin-1/2 Heisenberg Hamiltonian, we observe that the genuine multiparty entanglement in the system can either increase or counterintuitively diminish with a growing range of interactions. The behavior is reflective of the underlying phase structure of the quantum system and provides key insights for generation of multipartite entanglement in experimental atomic, molecular, and optical physics where such variable-range interactions have been implemented.
Roy SS, Dhar HS, SenDe A, et al., 2019, Tensor-network approach to compute genuine multisite entanglement in infinite quantum spin chains, PHYSICAL REVIEW A, Vol: 99, ISSN: 2469-9926
Roy SS, Dhar HS, Sen De A, et al., 2019, Fibonacci sequence and its generalizations in doped quantum spin ladders, Journal of Magnetism and Magnetic Materials, Vol: 478, Pages: 100-108, ISSN: 0304-8853
An interesting aspect of antiferromagnetic quantum spin ladders, with complete dimer coverings, is that the wave function can be recursively generated by estimating the number of coverings in the valence bond basis, which follow the fabled Fibonacci sequence. In this work, we derive generalized forms of this sequence for multi-legged and doped quantum spin ladders, which allow the corresponding dimer-covered state to be recursively generated. We show that these sequences allow for estimation of physically and information-theoretically relevant quantities in large spin lattices without resorting to complex numerical methods. We apply the formalism to calculate the valence bond entanglement entropy, which is an important figure of merit for studying cooperative phenomena in quantum spin systems with SU(2) symmetry. We show that introduction of doping may mitigate, within the quarters of entanglement entropy, the dichotomy between odd- and even- legged quantum spin ladders.
Dhar HS, Zens M, Krimer DO, et al., 2018, Variational renormalization group for dissipative spin-cavity systems: periodic pulses of nonclassical photons from mesoscopic spin ensembles, Physical Review Letters, Vol: 121, Pages: 133601-4-133601-7, ISSN: 0031-9007
Mesoscopic spin ensembles coupled to a cavity offer the exciting prospect of observing complex nonclassical phenomena that pool the microscopic features from a few spins with those of macroscopic spin ensembles. Here, we demonstrate how the collective interactions in an ensemble of as many as a hundred spins can be harnessed to obtain a periodic pulse train of nonclassical light. To unravel the full quantum dynamics and photon statistics, we develop a time-adaptive variational renormalization group method that accurately captures the underlying Lindbladian dynamics of the mesoscopic spin-cavity system.
Das S, Roy SS, Dhar HS, et al., 2018, Adiabatic freezing of entanglement with insertion of defects in a one-dimensional Hubbard model, Physical review B: Condensed matter and materials physics, Vol: 98, Pages: 125125-1-125125-7, ISSN: 1098-0121
We report on ground state phases of a doped one-dimensional Hubbard model, which for large onsite interactions is governed by the t−J Hamiltonian, where the extant entanglement is immutable under perturbative or sudden changes of system parameters, a phenomenon termed as adiabatic freezing. We observe that in the metallic Luttinger liquid phase of the model bipartite entanglement decays polynomially and is adiabatically frozen, in contrast to the variable, exponential decay in the phase-separation and superconducting spin-gap phases. Significantly, at low fixed electron densities, the spin-gap phase shows remarkable affinity to doped resonating valence bond gas, with multipartite entanglement frozen across all parameter space. We note that entanglement, in general, is sensitive to external perturbation, as observed in several systems, and hitherto, no such invariance or freezing behavior has been reported.
Roy SS, Dhar HS, Rakshit D, et al., 2018, Response to defects in multipartite and bipartite entanglement of isotropic quantum spin networks, PHYSICAL REVIEW A, Vol: 97, ISSN: 2469-9926
Pandit M, Das S, Roy SS, et al., 2018, Effects of cavity-cavity interaction on the entanglement dynamics of a generalized double Jaynes-Cummings model, Journal of Physics B: Atomic, Molecular and Optical Physics, Vol: 51, Pages: 1-7, ISSN: 0953-4075
We consider a generalized double Jaynes–Cummings model consisting of two isolated two-level atoms, each contained in a lossless cavity that interact with each other through a controlled photon-hopping mechanism. We analytically show that at low values of such a mediated cavity–cavity interaction, the temporal evolution of entanglement between the atoms, under the effects of cavity perturbation, exhibits the well-known phenomenon of entanglement sudden death (ESD). Interestingly, for moderately large interaction values, a complete preclusion of ESD is achieved, irrespective of its value in the initial atomic state. Our results provide a model to sustain entanglement between two atomic qubits, under the adverse effect of cavity induced perturbation, by introducing a non-intrusive inter-cavity photon exchange that can be physically realized through cavity-QED setups in contemporary experiments.
Roy SS, Dhar HS, Rakshit D, et al., 2017, Detecting phase boundaries of quantum spin-1/2 XXZ ladder via bipartite and multipartite entanglement transitions, Journal of Magnetism and Magnetic Materials, Vol: 444, Pages: 227-235, ISSN: 0304-8853
Phase transition in quantum many-body systems inevitably causes changes in certain physical properties which then serve as potential indicators of critical phenomena. Besides the traditional order parameters, characterization of quantum entanglement has proven to be a computationally efficient and successful method for detection of phase boundaries, especially in one-dimensional models. Here we determine the rich phase diagram of the ground states of a quantum spin-1/2 XXZ ladder by analyzing the variation of bipartite and multipartite entanglements. Our study characterizes the different ground state phases and notes the correspondence with known results, while highlighting the finer details that emerge from the behavior of ground state entanglement. Analysis of entanglement in the ground state provides a clearer picture of the complex ground state phase diagram of the system using only a moderate-size model.
Roy SS, Dhar HS, Rakshit D, et al., 2017, Analytical recursive method to ascertain multisite entanglement in doped quantum spin ladders, Physical review B: Condensed matter and materials physics, Vol: 96, Pages: 075143-1-075143-10, ISSN: 1098-0121
We formulate an analytical recursive method to generate the wave function of doped short-range resonating valence bond (RVB) states as a tool to efficiently estimate multisite entanglement as well as other physical quantities in doped quantum spin ladders. We prove that doped RVB ladder states are always genuine multipartite entangled. Importantly, our results show that within specific doping concentration and model parameter regimes, the doped RVB state essentially characterizes the trends of genuine multiparty entanglement in the exact ground states of the Hubbard model with large on-site interactions, in the limit that yields the t−J Hamiltonian.
Kumar A, Dhar HS, Prabhu R, et al., 2017, Forbidden regimes in the distribution of bipartite quantum correlations due to multiparty entanglement, PHYSICS LETTERS A, Vol: 381, Pages: 1701-1709, ISSN: 0375-9601
Dhar HS, Pal AK, Rakhsit D, et al., 2017, Lectures on general quantum correlations and their applications, Lectures on General Quantum Correlations and their Applications, Editors: Fanchini, Pinto, Adesso, Publisher: Springer International Publishing, Pages: 23-64, ISBN: 9783319534107
Monogamy is an intrinsic feature of quantum correlations that gives rise to several interesting quantum characteristics which are not amenable to classical explanations. The monogamy property imposes physical restrictions on unconditional sharability of quantum correlations between different parts of a multipartite quantum system, and thus has a direct bearing on the cooperative properties of multipartite states, including those of large many-body systems. On the contrary, a certain party can be maximally classical correlated with an arbitrary number of parties. In recent years, the monogamy property of quantum correlations has been applied to understand several key aspects of quantum physics, including distribution of quantum resources, security in quantum communication, critical phenomena, and quantum biology. In this chapter, we look at some of the salient developments and applications in quantum physics that have been closely associated with the monogamy of quantum discord, and “discord-like” quantum correlation measures.
Dhar HS, Rakshit D, Sen De A, et al., 2016, Adiabatic freezing of long-range quantum correlations in spin chains, EPL, Vol: 114, ISSN: 0295-5075
We consider a process to create quasi–long-range quantum discord between the non-interacting end spins of a quantum spin chain, with the end spins weakly coupled to the bulk of the chain. The process is not only capable of creating long-range quantum correlation but the latter remains frozen, when certain weak end-couplings are adiabatically varied below certain thresholds. We term this phenomenon as adiabatic freezing of quantum correlation. We observe that the freezing is robust to moderate thermal fluctuations and is intrinsically related to the cooperative properties of the quantum spin chain. In particular, we find that the energy gap of the system remains frozen for these adiabatic variations, and moreover, considering the end spins as probes, we show that the interval of freezing can detect the anisotropy transition in quantum XY spin chains. Importantly, the adiabatic freezing of long-range quantum correlations can be simulated with contemporary experimental techniques.
Kumar A, Dhar HS, 2016, Lower bounds on the violation of the monogamy inequality for quantum correlation measures, PHYSICAL REVIEW A, Vol: 93, ISSN: 2469-9926
Roy SS, Dhar HS, Rakshit D, et al., 2016, Diverging scaling with converging multisite entanglement in odd and even quantum Heisenberg ladders, NEW JOURNAL OF PHYSICS, Vol: 18, ISSN: 1367-2630
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- Citations: 6
Dhar HS, Chatterjee A, Ghosh R, 2015, Generating continuous variable entangled states for quantum teleportation using a superposition of number-conserving operations (vol 48, 185502, 2015), JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, Vol: 48, ISSN: 0953-4075
Souza LAM, Dhar HS, Nath Bera M, et al., 2015, Gaussian interferometric power as a measure of continuous-variable non-Markovianity, PHYSICAL REVIEW A, Vol: 92, ISSN: 2469-9926
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- Citations: 22
Dhar HS, Chatterjee A, Ghosh R, 2015, Generating continuous variable entangled states for quantum teleportation using a superposition of number-conserving operations, JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, Vol: 48, ISSN: 0953-4075
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- Citations: 9
Streltsov A, Singh U, Dhar HS, et al., 2015, Measuring Quantum Coherence with Entanglement, PHYSICAL REVIEW LETTERS, Vol: 115, ISSN: 0031-9007
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- Citations: 646
Singh U, Bera MN, Dhar HS, et al., 2015, Maximally coherent mixed states: Complementarity between maximal coherence and mixedness, PHYSICAL REVIEW A, Vol: 91, ISSN: 2469-9926
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- Citations: 124
Dhar HS, Bera MN, Adesso G, 2015, Characterizing non-Markovianity via quantum interferometric power, PHYSICAL REVIEW A, Vol: 91, ISSN: 1050-2947
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- Citations: 74
Singh U, Mishra U, Dhar HS, 2014, Enhancing robustness of multiparty quantum correlations using weak measurement, ANNALS OF PHYSICS, Vol: 350, Pages: 50-68, ISSN: 0003-4916
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- Citations: 9
Dhar HS, Chatterjee A, Ghosh R, 2014, Mapping generalized Jaynes-Cummings interaction into correlated finite-sized systems, JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, Vol: 47, ISSN: 0953-4075
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- Citations: 3
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