"We're delighted to learn that one of our own (Swati Singh) has won the NSF CAREER award (https://www.nsf.gov/awardsearch/showAward?AWD_ID=2047707). Many congratulations Swati and many happy returns"

# ITAMP News

Youtube: https://youtu.be/VcS_FznLURM

Guest Speaker: Professor Maxim Olshanii

Affiliation: University of Massachusetts Boston

Date: May 20, 2021

Time: 1:00 PM Eastern time

Triangular Gross-Pitaevskii breathers and Damski-Chandrasekhar shock waves

The recently proposed map [arXiv:2011.01415] between the hydrodynamic equations governing the two-dimensional triangular cold-bosonic breathers [Phys. Rev. X 9, 021035 (2019)] and the high-density zero-temperature triangular free-fermionic clouds, both trapped harmonically, perfectly explains the former phenomenon but leaves uninterpreted the nature of the initial (t=0) singularity. This singularity is a density discontinuity that leads, in the bosonic case, to an infinite force at the cloud edge. The map itself becomes invalid at time t=T/4. Here, we first map -- using the scale invariance of the problem -- the trapped motion to an untrapped one. Then we show that in the new representation, the solution [arXiv:2011.01415] becomes, along a ray in the direction normal to one of the three edges of the initial cloud, a freely propagating one-dimensional shock wave of a class proposed by Damski in [Phys. Rev. A 69, 043610 (2004)]. There, for a broad class of initial conditions, the one-dimensional hydrodynamic equations can be mapped to the inviscid Burgers' equation, a nonlinear transport equation. More specifically, under the Damski map, the t=0 singularity of the original problem becomes, verbatim, the initial condition for the wave catastrophe solution found by Chandrasekhar in 1943 [Ballistic Research Laboratory Report No. 423 (1943)]. At t=T/8, our interpretation ceases to exist: at this instance, all three effectively one-dimensional shock waves emanating from each of the three sides of the initial triangle collide at the origin, and the 2D-1D correspondence between the solution of [arXiv:2011.01415] and the Damski-Chandrasekhar shock wave becomes invalid.

Professor Hannes Bernien

University of Chicago

Location: Virtual meeting on Zoom

Date: May 6, 2021

Time: 1:00 PM Eastern time

New tools in the atom array toolbox: Dual species arrays and telecom operation

Reconfigurable arrays of neutral atoms are an exciting new platform to study quantum many-body phenomena and quantum information protocols. Their excellent coherence combined with programmable Rydberg interactions have led to intriguing observations such as quantum phase transitions, the discovery of quantum many-body scars, and the recent realization of a topological spin liquid phase.

Here, I will introduce new methods for controlling and measuring atom arrays that could open up new directions in quantum state control, quantum feedback and many-body physics. First, I will present our progress towards a dual species atomic array in which the second atomic species can be used to measure and control the primary species. This will lead to the possibility of performing quantum nondemolition measurements and new ways of engineering large, entangled states on these arrays. Furthermore, prospects of studying open systems with engineered environments will be discussed.

An alternative, hybrid approach for engineering interactions and scaling these quantum systems is the coupling of atoms to nanophotonic structures in which photons mediate interactions between atoms. Such a system can function as the building block of a large-scale quantum network. In this context, I will present quantum network node architectures that are capable of long-distance entanglement distribution at telecom wavelengths.

Rydberg systems: from the exotic to applications

Rydberg atoms has emerged as a versatile platform for different applications in quantum technology from computing and simulation to sensing and imaging [1]. In this talk, I will briefly mention the different Rydberg projects in Durham, and then focus on our recent work on Rydberg quantum optics. In this experiment, we store optical photons in a cold atomic ensemble in the form of Rydberg polaritons. In recent work, we have looked at the potential of Rydberg polaritons in the context of quantum information. We show that Rydberg polaritons have a number of attractive features: The large dipole moments between Rydberg states enables fast single-qubit rotations that are independent of atoms number. The combined atomic and photonic character of the polariton [2] allows fast photonic read-out of the quantum state. Finally, as the quantum information is shared amongst many atoms, there is an in-built robustness to atom loss [3]. Experiments on the extension to higher dimensions, photonic qutrits, will be presented.

References

[1] CS Adams et al, Rydberg atom quantum technologies, J Phys B 53, 012002 (2019).

[2] Y Jiao et al, Single-photon stored-light interferometry, Opt Lett 45, 5888 (2020).

[3]NLR Spong et al, The Robustness of a Collectively Encoded Rydberg Qubit, arXiv:2010.11794 (2020).

Taking the temperature of a pure quantum state

Temperature is a deceptively simple concept that still raises deep questions at the forefront of quantum physics research. The observation of thermalisation in completely isolated quantum systems, such as cold-atom quantum simulators, implies that a temperature can be assigned even to individual, pure quantum states. Here, we propose a scheme to measure the temperature of a pure state through quantum interference. Our proposal involves Ramsey interferometry of an auxiliary qubit probe, which is prepared in a superposition state and subsequently undergoes decoherence due to weak coupling with an isolated many-body system. Using only a few basic assumptions about chaotic quantum systems -- namely, the eigenstate thermalisation hypothesis and the equations of diffusive hydrodynamics -- we show that the qubit undergoes pure exponential decoherence at a rate that depends on the temperature of its surroundings. We verify our predictions by numerical experiments on a quantum spin chain that thermalises after absorbing energy from a periodic drive. Our work provides a general method to measure the temperature of isolated, strongly interacting systems under minimal assumptions.

Reference: https://arxiv.org/abs/2103.16601

Youtube:

https://youtu.be/h7LqxxYhmhc

Link to ITAMP During the Pandemic Seminars:

https://www.youtube.com/playlist?list=PLCoSh1h28ieL2m-Hq0ko5fiVkWPz6IeDi

The journal selected Nicole Yunger Halpern paper "Nonlinear Bell inequality for macroscopic measurements" for highlighting as an Editor's suggestion.

The quantum equivalent of seeing bacteria through everyday glasses

Entanglement—strong correlations that quantum particles can share— divides quantum physics from the everyday, or classical, world. Detecting entanglement in, for example, quantum computers and quantum networks is important: Only if nonclassical does a device have the potential to solve problems or to communicate information in ways impossible for today’s computers and telephones. Quantum systems are small, whereas classical systems are large. So conventional wisdom dictates that we can detect entanglement only if able to measure systems very precisely, similarly to how we can see bacteria only if given a microscope. This paper shows how to see bacteria through ordinary glasses, so to speak—how to detect entanglement amongst many particles by measuring only large-scale properties coarsely. The scheme works if the particles interact with each other in a limited fashion. Examples include detecting entanglement amongst photons (particles of light) by measuring the overall intensity of a beam of light. The photon proposal is testable in laboratories today; more- speculative applications include biochemistry and cosmology. This work challenges intuitions about the quantum-classical divide while helping us detect deviations from our everyday world.