More than 65 years ago, Jost and Kohn [R. Jost and W. Kohn, Phys. Rev. 87, 977 (1952)] derived an explicit expression for a class of short-range model potentials from a given effective range expansion with the s-wave scattering length as being negative. For as > 0, they calculated another class of short-range model potentials [R. Jost and W. Kohn, Dan. Mat. Fys. Medd 27, 1 (1953)] using a method based on an adaptation from Gelfand-Levitan theory [I. M. Gel'fand and B. M. Levitan, Dokl. Akad. Nauk. USSR 77, 557-560 (1951)] of inverse scattering. We here revisit the methods of Jost and Kohn in order to explore the possibility of modeling resonant finite-range interactions at low energy. We show that the Jost-Kohn potentials can account for zero-energy resonances. The s-wave phase shift for positive scattering length is expressed in an analytical form as a function of the binding energy of a bound state. We show that, for small binding energy, both the scattering length and the effective range are strongly influenced by the binding energy; and below a critical binding energy the effective range becomes negative provided the scattering length is large. As a consistency check, we carry out some simple calculations to show that Jost-Kohn potentials can reproduce the standard results of contact interaction in the limit of the effective range going to zero.

Abstract.In a previous paper [Das B et al. J. Phys. B: At. Mol. Opt. Phys 2013 46 035501], it was shown that the unitary quantum phase operators play a particularly important role in quantum dynamics of bosons and fermions in a one-dimensional double-well (DW) when the number of particles is small. In this paper, we define the standard quantum limit (SQL) for phase and number fluctuations, and describe two-mode squeezing for number and phase variables. The usual two-mode number squeezing parameter, also used to describe two-mode entanglement of a quantum field, is defined considering phase as a classical variable. However, when phase is treated as a unitary quantum-mechanical operator, number and phase operators satisfy an uncertainty relation. As a result, the usual definition of number squeezing parameter becomes modified. Twomode number squeezing occurs when the number fluctuation goes below the SQL at the cost of enhanced phase fluctuation. As an application of number-phase uncertainty, we consider bosons or fermions trapped in a quasi-one dimensional double-well (DW) potential interacting via a 3D finite-range two-body interaction potential with large scattering length a s . Under tight-binding or two-mode approximation, we describe in detail the effects of the range of interaction on the quantum dynamics and number-phase uncertainty in the strongly interacting or unitarity regime a s → ±∞. Our results show intriguing coherent dynamics of number-phase uncertainty with number-squeezing for bosons and phase squeezing for fermions. Our results may be important for exploring new quantum interferometry, Josephson oscillations, Bose-Hubbard and Fermi-Hubbard physics with ultracold atoms in DW potentials or DW optical lattices. Particularly interesting will be the question of the importance of quantum phase operators in two-atom interferometry and entanglement.Number-phase uncertainty and quantum dynamics of bosons and fermions interacting with a finite range and lar

We theoretically study the effects of trap-confinement and interatomic interactions on Josephson oscillations (JO) and macroscopic quantum self-trapping (MQST) for a Bose-Einstein condensate (BEC) confined in a trap which has a symmetric double-well (DW) potential along zaxis and 2D harmonic potentials along x-and y-axis. We consider three types of model interaction potentials: contact, long-range dipolar and finite-range potentials. Our results show that by changing the aspect ratio between the axial and radial trap sizes, one can induce a transition from JO to MQST for contact interactions with a small scattering length. For long-range dipolar interatomic interactions, we analyze transition from Rabi to Josephson regime and Josephson to MQST regime by changing the aspect ratio of the trap for a particular dipolar orientation. For a finite-range interaction, we study the effects of relatively large scattering length and effective range on JO and MQST. We show that JO and MQST are possible even if scattering length is relatively large, particularly near a narrow Feshbach resonance due to the finite-range effects.

No abstract

We investigate the steady-state quantum phases and associated collective phenomena of an open Tavis-Cummings (TC) model driven by a two-photon source. The standard (non-dissipative) TC model describes quantum phases of an ensemble of $N_q$ two-level quantum emitters interacting with a single-mode electromagnetic field. The interplay among coherent driving, dissipation, and dipole interactions of the open TC model results in emergent collective phenomena, leading to a dissipative or nonequilibrium phase transition from normal to superradiant phase. We solve the Liouvillian equation analytically using the semi-classical mean-field approximation. We carry out the stability analysis of the steady-state phases and determine the phase boundary. The use of Holstein-Primakoff transformation in the thermodynamic limit $N_q\rightarrow\infty$ reduces the system to an effective coupled-oscillator model, the solution of which yields collective modes.