Arxiv Selection Mar 2020

Mar 1- Mar 7 Bhaskar Mukherjee, Mar 8- Mar 14 Zehan Li, Mar 15- Mar 21 Haiping Hu, Mar 22- Mar 28 Sayan Choudhury

Mar 9

arXiv:2003.06921 [pdf, ps, other]

Projected Gross-Pitaevskii equation for ring-shaped Bose-Einstein condensates

O. O. Prikhodko, Y. M. Bidasyuk

Subjects: Quantum Gases (cond-mat.quant-gas)

We propose an alternative implementation of the Projected Gross-Pitaevskki equation adapted for numerical modeling of the atomic Bose-Einstein condensate trapped in a toroidally-shaped potential. We present an accurate and efficient scheme to evaluate the required matrix elements and calculate time evolution of the matter wave field. We analyze the stability and accuracy of the developed method for equilibrium and nonequilibrium solutions in a ring-shaped trap with additional barrier potential corresponding to recent experimental realizations.

Mar 10

arXiv:2003.07378 [pdf, other]

Ramsey interferometry of non-Hermitian quantum impurities

F. Tonielli, N. Chakraborty, F. Grusdt, J. Marino

Comments: 5+5 pages; 2 figures

Subjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)

We introduce a Ramsey pulse scheme which extracts the non-Hermitian Hamiltonian associated to an arbitrary Lindblad dynamics. We propose a realted protocol to measure via interferometry a generalised Loschmidt echo of a generic state evolving in time with the non-Hermitian Hamilto- nian itself, and we apply the scheme to a one-dimensional weakly interacting Bose gas coupled to a stochastic atomic impurity. The Loschmidt echo is mapped into a functional integral from which we calculate the long-time decohering dynamics at arbitrary impurity strengths. For strong dissipation we uncover the phenomenology of a quantum many-body Zeno effect: corrections to the decoher- ence exponent resulting from the impurity self-energy becomes purely imaginary, in contrast to the regime of small dissipation where they instead enhance the decay of quantum coherences. Our re- sults illustrate the prospects for experiments employing Ramsey interferometry to study dissipative quantum impurities in condensed matter and cold atoms systems.

Mar 11

arXiv:2003.06087 (cross-list from quant-ph) [pdf, other]

Protecting Spin Coherence in a Tunable Heisenberg Model

Emily J. Davis, Avikar Periwal, Eric S. Cooper, Gregory Bentsen, Simon J. Evered, Katherine Van Kirk, Monika H. Schleier-Smith

Using an ensemble of atoms in an optical cavity, we engineer a family of nonlocal Heisenberg Hamiltonians with continuously tunable anisotropy of the spin-spin couplings. We thus gain access to a rich phase diagram, including a paramagnetic-to-ferromagnetic Ising phase transition that manifests as a diverging magnetic susceptibility at the critical point. The susceptibility displays a symmetry between Ising interactions and XY (spin-exchange) interactions of the opposite sign, which is indicative of the spatially extended atomic system behaving as a single collective spin. Images of the magnetization dynamics show that spin-exchange interactions protect the coherence of the collective spin, even against inhomogeneous fields that completely dephase the non-interacting and Ising systems. Our results underscore prospects for harnessing spin-exchange interactions to enhance the robustness of spin squeezing protocols. Subjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas)

Mar 12

arXiv:2003.07873 [pdf, other]

On the low-energy description for tunnel-coupled one-dimensional Bose gases

Yuri D. van Nieuwkerk, Fabian H. L. Essler

Comments: 27 pages, 12 figures

Subjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)

We consider a model of two tunnel-coupled one-dimensional Bose gases with hard-wall boundary con- ditions. Bosonizing the model and retaining only the most relevant interactions leads to a decoupled theory consisting of a quantum sine-Gordon model and a free boson, describing respectively the anti- symmetric and symmetric combinations of the phase fields. We go beyond this description by retaining the perturbation with the next smallest scaling dimension. This perturbation carries conformal spin and couples the two sectors. We carry out a detailed investigation of the effects of this coupling on the non-equilibrium dynamics of the model. We focus in particular on the role played by spatial inhomogeneities in the initial state in a quantum quench setup.

Mar 13

arXiv:2003.08709 (cross-list from quant-ph) [pdf, other]

Atom-Photon Spin-Exchange Collisions Mediated by Rydberg Dressing

Fan Yang, Yong-Chun Liu, Li You

Comments: 6+6 pages, 4+3 figures

Subjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); Optics (physics.optics)

We show that photons propagating through a Rydberg-dressed atomic ensemble can exchange its spin state with a single atom. Such a spin-exchange collision exhibits both dissipative and coherent features, depending on the interaction strength. For strong interaction, the collision dissipatively drives the system into an entangled dark state of the photon with an atom. In the weak interaction regime, the scattering coherently flips the spin of a single photon in the multi-photon input pulse, demonstrating a generic single-photon subtracting process. An analytic analysis of this process reveals a universal trade-off between efficiency and purity of the extracted photon, which applies to a wide class of single-photon subtractors. We show that such a trade-off can be optimized by adjusting the scattering rate under a novel phase-matching condition.