Quantum interference of tunneling paths under a double-well barrier

The tunnel effect, a hallmark of the quantum realm, involves motion across a classically forbidden region. In a driven nonlinear system, two or more tunneling paths may coherently interfere, enhancing or cancelling the tunnel effect. Since individual quantum systems are difficult to control, this interference effect has only been studied for the lowest energy states of many-body ensembles. In our experiment, we show a coherent cancellation of the tunneling amplitude in the ground and excited state manifold of an individual squeeze-driven Kerr oscillator, a consequence of the destructive interference of tunneling paths in the classically forbidden region. The tunnel splitting vanishes periodically in the spectrum as a function of the frequency of the squeeze-drive, with the periodicity given by twice the Kerr coefficient. This resonant cancellation, combined with an overall exponential reduction of tunneling as a function of both amplitude and frequency of the squeeze-drive, reduces drastically the well-switching rate under incoherent environment-induced evolution. The control of tunneling via interference effects can be applied to quantum computation, molecular, and nuclear physics

Towards quantum simulation with circular Rydberg atoms

The main objective of quantum simulation is an in-depth understanding of many-body physics. It is important for fundamental issues (quantum phase transitions, transport, . . . ) and for the development of innovative materials. Analytic approaches to many-body systems are limited and the huge size of their Hilbert space makes numerical simulations on classical computers intractable. A quantum simulator avoids these limitations by transcribing the system of interest into another, with the same dynamics but with interaction parameters under control and with experimental access to all relevant observables. Quantum simulation of spin systems is being explored with trapped ions, neutral atoms and superconducting devices. We propose here a new paradigm for quantum simulation of spin-1/2 arrays providing unprecedented flexibility and allowing one to explore domains beyond the reach of other platforms. It is based on laser-trapped circular Rydberg atoms. Their long intrinsic lifetimes combined with the inhibition of their microwave spontaneous emission and their low sensitivity to collisions and photoionization make trapping lifetimes in the minute range realistic with state-of-the-art techniques. Ultra-cold defect-free circular atom chains can be prepared by a variant of the evaporative cooling method. This method also leads to the individual detection of arbitrary spin observables. The proposed simulator realizes an XXZ spin-1/2 Hamiltonian with nearest-neighbor couplings ranging from a few to tens of kHz. All the model parameters can be tuned at will, making a large range of simulations accessible. The system evolution can be followed over times in the range of seconds, long enough to be relevant for ground-state adiabatic preparation and for the study of thermalization, disorder or Floquet time crystals. This platform presents unrivaled features for quantum simulation