158 research outputs found
Microtraps for neutral atoms using superconducting structures in the critical state
Recently demonstrated superconducting atom-chips provide a platform for
trapping atoms and coupling them to solid-state quantum systems. Controlling
these devices requires a full understanding of the supercurrent distribution in
the trapping structures. For type-II superconductors, this distribution is
hysteretic in the critical state due to the partial penetration of the magnetic
field in the thin superconducting film through pinned vortices. We report here
an experimental observation of this memory effect. Our results are in good
agreement with the redictions of the Bean model of the critical state without
adjustable parameters. The memory effect allows to write and store permanent
currents in micron-sized superconducting structures and paves the way towards
new types of engineered trapping potentials.Comment: accepted in Phys. Rev.
Coherence-preserving trap architecture for long-term control of giant Rydberg atoms
We present a way to trap a single Rydberg atom, make it long-lived and
preserve an internal coherence over time scales reaching into the minute range.
We propose to trap using carefully designed electric fields, to inhibit the
spontaneous emission in a non resonant conducting structure and to maintain the
internal coherence through a tailoring of the atomic energies using an external
microwave field. We thoroughly identify and account for many causes of
imperfection in order to verify at each step the realism of our proposal.Comment: accepted for publication in PR
Real-time quantum feedback prepares and stabilizes photon number states
Feedback loops are at the heart of most classical control procedures. A
controller compares the signal measured by a sensor with the target value. It
adjusts then an actuator in order to stabilize the signal towards its target.
Generalizing this scheme to stabilize a micro-system's quantum state relies on
quantum feedback, which must overcome a fundamental difficulty: the
measurements by the sensor have a random back-action on the system. An optimal
compromise employs weak measurements providing partial information with minimal
perturbation. The controller should include the effect of this perturbation in
the computation of the actuator's unitary operation bringing the incrementally
perturbed state closer to the target. While some aspects of this scenario have
been experimentally demonstrated for the control of quantum or classical
micro-system variables, continuous feedback loop operations permanently
stabilizing quantum systems around a target state have not yet been realized.
We have implemented such a real-time stabilizing quantum feedback scheme. It
prepares on demand photon number states (Fock states) of a microwave field in a
superconducting cavity and subsequently reverses the effects of
decoherence-induced field quantum jumps. The sensor is a beam of atoms crossing
the cavity which repeatedly performs weak quantum non-demolition measurements
of the photon number. The controller is implemented in a real-time computer
commanding the injection, between measurements, of adjusted small classical
fields in the cavity. The microwave field is a quantum oscillator usable as a
quantum memory or as a quantum bus swapping information between atoms. By
demonstrating that active control can generate non-classical states of this
oscillator and combat their decoherence, this experiment is a significant step
towards the implementation of complex quantum information operations.Comment: 12 pages, 4 figure
The Casimir force for passive mirrors
We show that the Casimir force between mirrors with arbitrary frequency
dependent reflectivities obeys bounds due to causality and passivity
properties. The force is always smaller than the Casimir force between two
perfectly reflecting mirrors. For narrow-band mirrors in particular, the force
is found to decrease with the mirrors bandwidth.Comment: 12 pages, 2 figures, LaTe
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
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