Arxiv Selection Sep 2019

Sep 1-Sep 7 Bhaskar Mukherjee, Sep 8- Sep 14 Sayan Choudhury, Sep 15- Sep 21 Zehan Li, Sep 22 - Sep 28 Jiansong Pan

Sep 20

arXiv:1909.09082 [pdf, other]

Supersolid stripe crystal from finite-range interactions on a lattice

Guido Masella, Adriano Angelone, Fabio Mezzacapo, Guido Pupillo, Nikolay V. Prokof'ev

Comments: 6+3 pages, 5+4 figures

Journal-ref: Phys. Rev. Lett. 123, 045301 (2019)

Subjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el)

Strong, long-range interactions present a unique challenge for the theoretical investigation of quantum many-body lattice models, due to the generation of large numbers of competing states at low energy. Here, we investigate a class of extended bosonic Hubbard models with off-site terms interpolating between short- and infinite-range, thus allowing for an exact numerical solution for all interaction strengths. We predict a novel type of stripe crystal at strong coupling. Most interestingly, for intermediate interaction strengths we demonstrate that the stripes can turn superfluid, thus leading to a self-assembled array of quasi one-dimensional superfluids. These bosonic superstripes turn into an isotropic supersolid with decreasing the interaction strength. The mechanism for stripe formation is based on cluster self-assemblying in the corresponding classical ground state, reminiscent of classical soft-matter models of polymers, different from recently proposed mechanisms for cold gases of alkali or dipolar magnetic atoms.

Sep 19

arXiv:1909.08225 [pdf, ps, other]

Symmetry breaking and entropy production during the evolution of spinor Bose-Einstein condensate driven by coherent atom beam

Yixin Xu, Zhongda Zeng, Zbignew Domanski, Zhibing Li

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

The spinor condensate with spin states degenerated in the ground spin-space provides a unique platform for investigating the edge of quantum mechanics and statistical physics. We study the evolution of the condensate under the scattering of a coherent atom beam. The time-dependent magnetization, entanglement entropy, thermal entropy, and the entropy production rate are calculated. A novel spontaneous symmetry breaking is found during the evolution. It is shown that the stationary spin distribution can be controlled by the incoming coherent spin state of the incident atom beam, therefore the atom-condensate scattering provides a new way to probe the spin distribution of the condensate.

Sep 18

arXiv:1909.07641 [pdf, other]

Realizing a scalable building block of a U(1) gauge theory with cold atomic mixtures

Alexander Mil, Torsten V. Zache, Apoorva Hegde, Andy Xia, Rohit P. Bhatt, Markus K. Oberthaler, Philipp Hauke, Jürgen Berges, Fred Jendrzejewski

Subjects: Quantum Gases (cond-mat.quant-gas); High Energy Physics - Phenomenology (hep-ph); Atomic Physics (physics.atom-ph); Quantum Physics (quant-ph)

In the fundamental laws of physics, gauge fields mediate the interaction between charged particles. An example is quantum electrodynamics—the theory of electrons interacting with the electromagnetic field—based on U(1) gauge symmetry. Solving such gauge theories is in general a hard problem for classical computational techniques. While quantum computers suggest a way forward, it is difficult to build large-scale digital quantum devices required for complex simulations. Here, we propose a fully scalable analog quantum simulator of a U(1) gauge theory in one spatial dimension. To engineer the local gauge symmetry, we employ inter-species spin-changing collisions in an atomic mixture. We demonstrate the experimental realization of the elementary building block as a key step towards a platform for large-scale quantum simulations of continuous gauge theories.

Sep 17

arXiv:1909.07358 [pdf, other]

Zero temperature momentum distribution of an impurity in one-dimensional Fermi and Tonks-Girardeau gases

Oleksandr Gamayun, Oleg Lychkovskiy, Mikhail B. Zvonarev

Comments: 37 pages, 10 figures

Subjects: Quantum Gases (cond-mat.quant-gas); Exactly Solvable and Integrable Systems (nlin.SI); Quantum Physics (quant-ph)

We investigate the momentum distribution function of a single distinguishable impurity particle immersed in a gas of either free fermions or Tonks-Girardeau bosons in one spatial dimension. We obtain a Fredholm determinant representation of the distribution function for the Bethe ansatz solvable model of an impurity-gas δ-function interaction potential at zero temperature, in both repulsive and attractive regimes. We deduce from this representation the fourth power decay at a large momentum, and a weakly divergent (quasi-condensate) peak at a finite momentum. We also demonstrate that the momentum distribution function in the limiting case of infinitely strong interaction can be expressed through a correlation function of the one-dimensional impenetrable anyons.

Sep 16

arXiv:1909.06050 [pdf, ps, other]

Superfluid weight and polarization amplitude in the one-dimensional bosonic Hubbard model

B. Hetényi, L.M. Martelo, B. Tanatar

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

We calculate the superfluid weight and the polarization amplitude for the one-dimensional bosonic Hubbard model focusing on the strong-coupling regime. Other than analytic calculations we apply two methods: variational Monte Carlo based on the Baeriswyl wave function and exact diagonalization. The former gives zero superfluid response at integer filling, while the latter gives a superfluid response at finite hopping. From the polarization amplitude we derive the variance and the associated size scaling exponent. Again, the variational study does not produce a finite superfluid weight at integer filling (size scaling exponent is near one), but the Fourier transform of the polarization amplitude behaves in a similar way to the result of exact diagonalization, with a peak at small hopping, and suddenly decreasing at the insulator-superfluid transition. On the other hand, exact diagonalization studies result in a finite spread of the total position which increases with the size of the system. In the superfluid phase the size scaling exponent is two as expected. Importantly, our work addresses the ambiguities that arise in the calculation of the superfluid weight in variational calculations, and we comment on the prediction of Anderson about the superfluid response of the model at integer filling.

Sep 15

arXiv:1909.05183 [pdf, other]

Many-Body Echo

Yang-Yang Chen, Pengfei Zhang, Wei Zheng, Zhigang Wu, Hui Zhai

Comments: 5 pages, 3 figures

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

In this letter we propose a protocol to reverse a quantum many-body dynamical process. We name it “many-body echo” because the underlying physics is closely related to the spin echo effect in nuclear magnetic resonance systems. We consider a periodical modulation of the interaction strength in a weakly interacting Bose condensate, which resonantly excites quasi-particles from the condensate. A dramatic phenomenon is that, after pausing the interaction modulation for half a period and then continuing on with the same modulation, nearly all the excited quasi-particles in the resonance modes will be absorbed back into the condensate. During the intermediate half period, the free evolution introduces a π phase, which plays a role reminiscent of that played by the π-pulse in the spin echo. Comparing our protocol with another one implemented by the Chicago group in a recent experiment, we find that ours is more effective at reversing the many-body process. The difference between these two schemes manifests the physical effect of the micro-motion in the Floquet theory. Our scheme can be generalized to other periodically driven many-body systems.

1) arXiv:1707.04344

Probing many-body dynamics on a 51-atom quantum simulator .

Authors: Hannes Bernien, Sylvain Schwartz, Alexander Keesling, Harry Levine, Ahmed Omran, Hannes Pichler, Soonwon Choi, Alexander S. Zibrov, Manuel Endres, Markus Greiner, Vladan Vuletić, Mikhail D. Lukin 

Abstract: Controllable, coherent many-body systems can provide insights into the fundamental properties of quantum matter, enable the realization of new quantum phases and could ultimately lead to computational systems that outperform existing computers based on classical approaches. Here we demonstrate a method for creating controlled many-body quantum matter that combines deterministically prepared, reconfigurable arrays of individually trapped cold atoms with strong, coherent interactions enabled by excitation to Rydberg states. We realize a programmable Ising-type quantum spin model with tunable interactions and system sizes of up to 51 qubits. Within this model, we observe phase transitions into spatially ordered states that break various discrete symmetries, verify the high-fidelity preparation of these states and investigate the dynamics across the phase transition in large arrays of atoms. In particular, we observe robust manybody dynamics corresponding to persistent oscillations of the order after a rapid quantum quench that results from a sudden transition across the phase boundary. Our method provides a way of exploring many-body phenomena on a programmable quantum simulator and could enable realizations of new quantum algorithms.

Comments: 17 pages, 13 figures

Journal ref: Nature 551, 579-584 (2017)

2) arXiv:1711.03528 .

Quantum many-body scars.

Authors: Christopher J. Turner, Alexios A. Michailidis, Dmitry A. Abanin, Maksym Serbyn, Zlatko Papic

Abstract: Certain wave functions of non-interacting quantum chaotic systems can exhibit "scars" in the fabric of their real-space density profile. Quantum scarred wave functions concentrate in the vicinity of unstable periodic classical trajectories. We introduce the notion of many-body quantum scars which reflect the existence of a subset of special many-body eigenstates concentrated in certain parts of the Hilbert space. We demonstrate the existence of scars in the Fibonacci chain -- the one- dimensional model with a constrained local Hilbert space realized in the 51 Rydberg atom quantum simulator [H. Bernien et al., arXiv:1707.04344]. The quantum scarred eigenstates are embedded throughout the thermalizing many-body spectrum, but surprisingly lead to direct experimental signatures such as robust oscillations following a quench from a charge-density wave state found in experiment. We develop a model based on a single particle hopping on the Hilbert space graph, which quantitatively captures the scarred wave functions up to large systems of L = 32 atoms. Our results suggest that scarred many-body bands give rise to a new universality class of quantum dynamics, which opens up opportunities for creating and manipulating novel states with long-lived coherence in systems that are now amenable to experimental study.