DSpace Collection:
http://hdl.handle.net/2289/144
2020-06-25T05:59:40ZAmplification and cross-Kerr nonlinearity in waveguide quantum electrodynamics
http://hdl.handle.net/2289/7477
Title: Amplification and cross-Kerr nonlinearity in waveguide quantum electrodynamics
Authors: Vinu, Athul; Roy, Dibyendu
Abstract: We explore amplification and cross-Kerr nonlinearity by a three-level emitter (3LE) embedded in a waveguide and driven by two light beams. The coherent amplification and cross-Kerr nonlinearity were demonstrated in recent experiments, respectively, with a V and a ladder-type 3LE coupled to an open superconducting transmission line carrying two microwave fields. Here, we consider Λ ,V , and ladder-type 3LE, and compare the efficiency of coherent and incoherent amplification as well as the magnitude of the cross-Kerr phase shift in all three emitters. We apply the Heisenberg-Langevin equations approach to investigate the scattering of a probe and a drive beam, both initially in coherent states. We particularly calculate the regime of the probe and drive powers when the 3LE acts most efficiently as a coherent amplifier and derive the second-order coherence of amplified probe photons. Finally, we apply the Kramers-Kronig relations to correlate the amplitude and phase response of the probe beam, which are used in finding the coherent amplification and the cross-Kerr phase shift in these systems
Description: Open Access2020-05-01T00:00:00ZLikelihood theory in a quantum world: Tests with quantum coins and computers
http://hdl.handle.net/2289/7464
Title: Likelihood theory in a quantum world: Tests with quantum coins and computers
Authors: Maitra, Arpita; Samuel, J.; Sinha, Supurna
Abstract: By repeated trials, one can determine the fairness of a classical coin with a confidence which grows
with the number of trials. A quantum coin can be in a superposition of heads and tails and its state is most generally a density matrix. Given a string of qubits representing a series of trials, one can measure them individually and determine the state with a certain confidence. We show that there is an improved strategy which measures the qubits after entangling them, which leads to a greater confidence. This strategy is demonstrated on the simulation facility of IBM quantum computers.
Description: Open Access2020-03-01T00:00:00ZDynamical correlations of conserved quantities in the one-dimensional equal mass hard particle gas
http://hdl.handle.net/2289/7455
Title: Dynamical correlations of conserved quantities in the one-dimensional equal mass hard particle gas
Authors: Kundu, Aritra; Dhar, Abhishek; Sabhapandit, Sanjib
Abstract: We study a gas of point particles with hard-core repulsion in one dimension where the particles move freely in-between elastic collisions. We prepare the system with a uniform density on the infinite line. The velocities {vi;i∈Z} of the particles are chosen independently from a thermal distribution. Using a mapping to the non-interacting gas, we analytically compute the equilibrium spatio-temporal correlations ⟨vmi(t)vnj(0)⟩ for arbitrary integers m,n . The analytical results are verified with microscopic simulations of the Hamiltonian dynamics. The correlation functions have ballistic scaling, as expected in an integrable model.
Description: Restricted Access.2020-02-19T00:00:00ZExact stationary state of a run-and-tumble particle with three internal states in a harmonic trap
http://hdl.handle.net/2289/7454
Title: Exact stationary state of a run-and-tumble particle with three internal states in a harmonic trap
Authors: Basu, Urna; Majumdar, Satya N; Sabhapandit, Sanjib; +2 Co-Authors
Abstract: We study the motion of a one-dimensional run-and-tumble particle with three discrete internal states in the presence of a harmonic trap of stiffness [ image ] The three internal states, corresponding to positive, negative and zero velocities respectively, evolve following a jump process with rate [ image ]. We compute the stationary position distribution exactly for arbitrary values of [ image ] and [ image ] which turns out to have a finite support on the real line. We show that the distribution undergoes a shape-transition as [ image ] is changed. For [ image ] the distribution has a double-concave shape and shows algebraic divergences with an exponent [ image ] both at the origin and at the boundaries. For [ image ] the position distribution becomes convex, vanishing at the boundaries and with a single, finite, peak at the origin. We also show that for the special case [ image ] the distribution shows a logarithmic divergence near the origin while saturating to a constant value at the boundaries.
Description: Restricted Access.2020-02-04T00:00:00Z