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Varad R. Pande

Publications and source records attributed to Varad R. Pande.

7 recordsLinked to original sources
arXiv2025

Analysis of exciton-polariton condensation under different pumping schemes for 1D and 2D microcavities including the effect of strong correlation between polaritons

Strongly correlated polaritons are necessary for entering the quantum photonic regime with many applications. We simulate exciton-polariton condensation using the finite-difference and 4th order Runge-Kutta methods with the strongly correlated polariton condition incorporated in the mean-field equations and analyze the polariton dynamics. This is done for coherent, near-resonant pumping as well as homogeneous, incoherent, non-resonant pumping. We find conditions akin to the polariton blockade in the dynamics.

quant-ph↗
arXiv2022

Optimal Entropy Compression and Purification in Quantum Bits

Global unitary transformations (OPTSWAPS) that optimally increase the bias of any mixed computation qubit in a quantum system -- represented by a diagonal density matrix -- towards a particular state of the computational basis which, in effect, increases its purity are presented. Quantum circuits that achieve this by implementing the above data compression technique -- a generalization of the 3B-Comp used before -- are described. These circuits enable purity increment in the computation qubit by maximally transferring part of its von Neumann or Shannon entropy to any number of surrounding qubits and are valid for the complete range of initial biases. Using the optswaps, a practicable new method that algorithmically achieves hierarchy-dependent cooling of qubits to their respective limits in an engineered quantum register opened to the heat-bath is delineated. In addition to multi-qubit purification and satisfying two of DiVincenzo's criteria for quantum computation in some architectures, the implications of this work for quantum data compression and quantum thermodynamics are discussed.

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arXiv2022

Quantum information transfer using weak measurements and any non-product resource state

Information about an unknown quantum state can be encoded in weak values of projectors belonging to a complete eigenbasis. We present a protocol that enables one party -- Bob -- to remotely determine the weak values corresponding to weak measurements performed by another spatially separated party -- Alice. The particular set of weak values contains complete information of the quantum state encoded on Alice's register, which enacts the role of preselected system state in the aforementioned weak measurement. Consequently, Bob can determine the quantum state from these weak values, which can also be termed as remote state determination or remote state tomography. A combination of non-product bipartite resource state shared between the two parties and classical communication between them is necessary to bring this statistical scheme to fruition. Significantly, the information transfer of a pure quantum state of any known dimensions can be effected even with resource states of low dimensionality and purity with a single measurement setting at Bob's end. Keywords: Remote state determination; Quantum communication; Non-classical correlations; Weak Values; Quantum resource states; Quantum teleportation; Quantum key distribution (QKD).

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arXiv2020

Simulating the effect of weak measurements by a phase damping channel and determining different measures of bipartite correlations in nuclear magnetic resonance

Quantum discord is a measure based on local projective measurements which captures quantum correlations that may not be fully captured by entanglement. A change in the measurement process, achieved by replacing rank-one projectors with a weak positive operator-valued measure (POVM), allows one to define weak variants of quantum discord. In this work, we experimentally simulate the effect of a weak POVM on a nuclear magnetic resonance quantum information processor. The two-qubit system under investigation is part of a three-qubit system, where one of the qubits is used as an ancillary to implement the phase damping channel. The strength of the weak POVM is controlled by varying the strength of the phase damping channel. We experimentally observed two weak variants of quantum discord namely, super quantum discord and weak quantum discord, in two-qubit Werner and Bell-diagonal states. The resultant dynamics of the states is investigated as a function of the measurement strength.

quant-ph↗
arXiv2017

Strong Algorithmic Cooling in Large Star-Topology Quantum Registers

Cooling the qubit into a pure initial state is crucial for realizing fault-tolerant quantum information processing. Here we envisage a star-topology arrangement of reset and computation qubits for this purpose. The reset qubits cool or purify the computation qubit by transferring its entropy to a heat-bath with the help of a heat-bath algorithmic cooling procedure. By combining standard NMR methods with powerful quantum control techniques, we cool central qubits of two large star topology systems, with 13 and 37 spins respectively. We obtain polarization enhancements by a factor of over 24, and an associated reduction in the spin temperature from 298 K down to 12 K. Exploiting the enhanced polarization of computation qubit, we prepare combination-coherences of orders up to 15. By benchmarking the decay of these coherences we investigate the underlying noise process. Further, we also cool a pair of computation qubits and subsequently prepare them in an effective pure-state.

quant-ph↗
arXiv2017

Minimum Disturbance Rewards with Maximum Possible Classical Correlations

Weak measurements done on a subsystem of a bipartite system having both classical and nonClassical correlations between its components can potentially reveal information about the other subsystem with minimal disturbance to the overall state. We use weak quantum discord and the fidelity between the initial bipartite state and the state after measurement to construct a cost function that accounts for both the amount of information revealed about the other system as well as the disturbance to the overall state. We investigate the behaviour of the cost function for families of two qubit states and show that there is an optimal choice that can be made for the strength of the weak measurement.

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