Sujit Sarkar

Collapse and revival of entanglement of two-qubit in superconducting quantum dot lattice with magnetic flux and inhomogeneous gate voltage

We study the entanglement of a two-qubit system in a superconducting quantum dot (SQD) lattice in the presence of magnetic flux and gate voltage inhomogeneity. We observe a universal feature for the half-integer magnetic flux quantum which completely washes out the entanglement of the system both at zero and finite temperature. We observe that the ground state is always in a maximally entangled Bell state when there is no inhomogeneity in gate voltage in the superconducting quantum dot lattice. We find an important constraint in magnetic flux for ground state entanglement. We also observe few behavior of entanglement at finite temperature is in contrast with the zero temperature behavior.

Quantum criticality of geometric phase in coupled optical cavity arrays under linear quench

Abstract The atoms trapped in microcavities and interacting through the exchange of virtual photons can be modeled as an anisotropic Heisenberg spin-1/2 lattice. We study the dynamics of the geometric phase of this system under the linear quenching process of laser field detuning, which shows XX criticality of the geometric phase and also gives the result of quantum criticality for different quenching rates.

Quantum spin pumping at a fractionally quantized magnetization state for a system with competing exchange interactions

We study the quantum spin pumping of an antiferromagnetic spin-1/2 chain with competing exchange interactions. We show that spatially periodic potential modulated in space and time acts as a quantum spin pump. In our model system, an applied electric field causes a spin gap to its critical ground state by introducing bond-alternation exchange interactions. We study quantum spin pumping at different quantized magnetization states and also explain physically the presence and absence of quantum spin pumping at different fractionally quantized magnetization states.

Existence of Majorana fermion mode and Dirac equation in cavity quantum electrodynamics

We present the results of low lying excitation of coupled optical cavity arrays. We derive the Dirac equation for this system and explain the existence of Majorana fermion mode in the system. We present quite a few analytical relations between the Rabi frequency oscillation and the atom-photon coupling strength to achieve the different physical situation of our study and also the condition for massless excitation in the system. We present several analytical relations between the Dirac spinor field, order and disorder operators for our systems. We also show that the Luttinger liquid physics is one of the intrinsic concept in our system.

Quantum phase transition in an array of coupled superconducting quantum dots with charge frustration

We present the quantum phase transition in two capacitively coupled arrays of superconducting quantum dots (SQD). We consider the presence of gate voltage in each superconducting island. We show explicitly that the co-tunneling process involves with two coupled SQD arrays, near the maximum charge frustration line is not sufficient to explain the correct quantum phases with physically consistent phase boundaries. We consider another extra co-tunneling process along each chain to explain the correct quantum phases with physically consistent phase boundaries. There is no evidence of supersolid phase in our study. We use Bethe-ansatz and Abelian bosonization method to solve the problem

Adiabatic Cooper-pair pumping in a linear array of Cooper-pair boxes

We present a study of adiabatic Cooper pair pumping in one dimensional array of Cooper pair boxes. We do a detailed theoretical analysis of an experimentally realizable stabilized charge pumping scheme in a linear array of Cooper pair boxes. Our system is subjected to synchronized flux and voltage fields and travel along a loop which encloses their critical ground state of the system in the flux-voltage plane. The locking potential in the sine-Gordon model slides and changes its minimum which yields the Cooper pair pumping. Our analytical methods are the Berry phase analysis and Abelian bosonization studies.

Quantum spin pumping for a system with competing exchange interactions

We study the quantum spin pumping of an antiferromagnetic spin‐1/2 chain with competing exchange interactions. We show that spatially periodic potential modulated in space and time acts as a quantum spin pump. In our model system, an applied electric field causes a spin gap to its critical ground state by introducing bond‐alternation exchange interactions.

Isotope-shift exponent and the gap ratio within the extended saddle point singularity scenario for different pairing symmetries

Abstract Exact analytical expressions for the isotope-shift exponent are derived within the BCS formalism for different pairing symmetries (isotropic s -wave, extended s -wave, d -wave) and extended saddle point singularity in the density of states (DOS) is considered. The isotope-shift exponent and the gap ratio are studied as a function of doping for different symmetries. It is found that the predictions for the d -wave pairing symmetry are closer to the experimental situation in cuprates.

The superconducting gap ratio, isotope-shift exponent and pressure coefficient of Tc for high-Tc systems

Abstract The superconducting gap ratio, isotope-shift exponent and the pressure co-efficient of the superconducting transition temperature are studied within different models proposed for high- T c cuprate oxide systems. A comparison with the experimental results of high- T c oxide systems is made.