
Chair: Fabian Essler

09:00  09:40

Steven Girvin
(Yale University)
Proposal to use QND photon number measurements to accelerate axion dark matter searches

09:40  10:20

Ana Maria Rey
(JILA, University of Colorado)
Dynamics of interacting fermions under spinorbit coupling in an optical lattice clock
The Pauli exclusion principle forbids identical fermions from interacting via swave collisions. However, in the presence of spinorbit coupling, identical fermions can experience effective interactions which can give rise to exotic topological and pairing behaviors, many of which have yet to be observed in condensed matter systems. Spinorbit coupled alkalineearth gases offer a promising pathway for quantum simulation of SOC physics given their longlived electronic clock states which significantly reduce spontaneous emission and heating, as has been demonstrated in recent experiment. However, these first experiments were carried out in the dilute regime where singleparticle physics dominates. Here I will report recent progress in one dimensional optical lattice clocks to enter the regime where interactions compete with singleparticle effects. We perform timeresolved and controlled measurements of collective manybody dynamics after a sudden quench in a nuclear spin polarized 87Sr gas with an effective spin degree of freedom encoded in the clock states. Using Ramsey spectroscopy we observe a precession of the collective magnetization and signatures of spin locking effects arising from an interplay between pwave and SOC induced swave interactions. The spin dynamics are well captured by a collective XXZ spin model that describes a broad class of condensed matter systems ranging from superconductors to quantum magnets.

10:20  10:50

coffee


Chair: Steven Girvin

10:50  11:30

Fabian Essler
(Oxford University)
Full counting statistics in the spin1/2 Heisenberg XXZ chain

11:30  12:10

Philipp Hauke
(Heidelberg University)
Quantum Fisher Information and Multiquantum Coherences as efficient entanglement witnesses in quantum manybody systems

12:10  12:25

Cristian Bonato
(HeriotWatt University)
Adaptive quantum sensing with spins in diamond
Sensors based on single spins can enable magnetic field detection with very
high sensitivity and spatial resolution.
The key challenge in sensing is to achieve minimum estimation uncertainty within a given time and with a high dynamic range. Adaptive strategies have been proposed to achieve optimal performance but their implementation in solidstate systems has been hindered by the demanding experimental requirements.
Here, I will report on our recent demonstration of adaptive sensing of a constant field, using a single electronic spin in a nitrogenvacancy center in diamond. By adapting the spin readout basis in real time based on previous outcomes we report a sensitivity in Ramsey interferometry surpassing the standard measurement limit. By numerical simulations and experiments, we find that adaptive protocols offer a distinctive advantage over the bestknown nonadaptive protocols when overhead and limited estimation time are taken into account.
Additionally, I will discuss an adaptive protocol, based on Bayesian estimation, to a track a field with nonperiodic variation described by a Wiener process. The tracking protocol updates the probability distribution for the magnetic field, based on measurement outcomes, and adapts the choice of sensing time and phase in real time. By taking the statistical properties of the signal into account, our protocol strongly reduces the required measurement time, reducing the error in the estimation of a timevarying signal by up to a factor 4.

12:25  15:00

lunch


Chair: Ana Maria Rey

15:00  15:40

Michael Hartmann
(HeriotWatt University)
Superconducting Quantum Simulator for Topological Order and the Toric Code
Topological order is now being established as a central criterion for characterizing and classifying ground states of condensed matter systems and complements categorizations based on symmetries. Fractional quantum Hall systems and quantum spin liquids are receiving substantial interest because of their intriguing quantum correlations, their exotic excitations and prospects for protecting stored quantum information against errors.
In this talk I will discuss our recent approach for implementing the Hamiltonian of the central model of this class of systems, the Toric Code, in lattices of superconducting circuits. The fourbody interactions, which lie at its heart, are in our concept realised via Superconducting Quantum Interference Devices (SQUIDs) driven by a suitably oscillating flux bias. All physical qubits can be individually controlled and strings of operators acting on them, including the stabilizers, can be read out via a capacitive coupling to common transmission line resonators. The architecture we propose thus provides a versatile quantum simulator for topological order and lattice gauge theories.
M. Sameti, A Potocnik, D. E. Browne, A. Wallraff, and M. J. Hartmann, Phys. Rev. A 95, 042330 (2017)

15:40  16:10

Soonwon Choi
(Harvard University)
Quantum manybody dynamics in strongly interacting dipolar spin systems: from timecrystals to quantum metrology
The interplay between periodic driving, disorder, and strong interactions has been predicted to result in exotic time crystalline phases, which spontaneously break the discrete timetranslation symmetry of the underlying drive. In this talk, I will present the experimental observation of such discrete time crystalline order in a driven, disordered ensemble of dipolar spin impurities in diamond at room temperature. We observe longlived temporal correlations, experimentally identify the phase boundary and find that the temporal order is protected by strong interactions. We quantitatively explain these observations using resonance counting, which reveals critically slow thermalization dynamics as the origin of the observed long lived order. Finally, I will discuss how such strongly interacting, driven manybody systems can be harnessed for quantum enhanced metrology.

16:10  16:30

coffee

16:30  17:00

Marine Pigneur
(TU Wien)
Sqeezing and relaxation in tunnel coupled 1D superfluids
We experimentally investigate the tunneling dynamics between two 1D quasi BoseEinstein condensates (1DBEC) of 87Rb, magnetically trapped on an atom chip. The presence of interatomic interaction in our system makes its dynamics of strong interest as it allows the generation of numbersqueezed states [1] and presents a relaxation through a mechanism still to be determined.
The realization of numbersqueezed states is presented in a first part of the talk. Starting with a single 1DBEC, we perform an adiabatic deformation of the trap by radiofrequency dressing and obtain two 1DBEC by splitting of the wave function. We demonstrated that interatomic interaction and tunneling during the splitting reduce the fluctuation of the atom number difference by 60% compared to a coherent state. The reduced number fluctuations and the very high coherence in our system lead to a 8 dB of spin squeezing, corresponding to the entanglement of about 10% of our atoms.
In a second part of the talk, we make use of the possibility to imprint a global relative phase between the superfluids to investigate the tunneling dynamics for various coupling strengths. The observed dynamics exhibits a rapid relaxation toward a phaselocked equilibrium state, which goes beyond the 3D predictions of the two site BoseHubbard model. We currently include this relaxation as an empirical friction to investigate the dependence of the damping magnitude with our experimental parameters. It results that the relaxation does not depend on the tunnel coupling and depends on the atom number as N1/2. We currently search for a relaxation mechanism compatible with our experimental observations.
As the relaxation occurs with a time scale comparable with the splitting time presented in the first part of this talk, we expect that it plays a role in the generation of numbersqueezing.
[1] T. Berrada, S. van Frank, R. Bücker, T. Schumm, J.F. Schaff & J. Schmiedmayer, Integrated MachZehnder interferometer for BoseEinstein condensates, Nature Communications, 4, 2077 (2013).

18:00

supper
