15 research outputs found
Echo Spectroscopy of Atomic Dynamics in a Gaussian Trap via Phase Imprints
We report on the collapse and revival of Ramsey fringe visibility when a
spatially dependent phase is imprinted in the coherences of a trapped ensemble
of two-level atoms. The phase is imprinted via the light shift from a Gaussian
laser beam which couples the dynamics of internal and external degrees of
freedom for the atoms in an echo spectroscopy sequence. The observed revivals
are directly linked to the oscillatory motion of atoms in the trap. An
understanding of the effect is important for quantum state engineering of
trapped atoms
Inhomogeneous Light Shift Effects on Atomic Quantum State Evolution in Non-Destructive Measurements
Various parameters of a trapped collection of cold and ultracold atoms can be
determined non--destructively by measuring the phase shift of an off--resonant
probe beam, caused by the state dependent index of refraction of the atoms. The
dispersive light--atom interaction, however, gives rise to a differential light
shift (AC Stark shift) between the atomic states which, for a nonuniform probe
intensity distribution, causes an inhomogeneous dephasing between the atoms. In
this paper, we investigate the effects of this inhomogeneous light shift in
non--destructive measurement schemes. We interpret our experimental data on
dispersively probed Rabi oscillations and Ramsey fringes in terms of a simple
light shift model which is shown to describe the observed behavior well.
Furthermore, we show that by using spin echo techniques, the inhomogeneous
phase shift distribution between the two clock levels can be reversed.Comment: 9 pages, 7 figures, updated introduction and reference lis
Ultra-coherent nanomechanical resonators based on inverse design
Engineered micro- and nanomechanical resonators with ultra-low dissipation
constitute the ideal systems for applications ranging from high-precision
sensing such as magnetic resonance force microscopy, to quantum transduction
between disparate quantum systems. Traditionally, the improvement of the
resonator's performance - often quantified by its Qf product (where Q is
quality factor and f is frequency) - through nanomechanical engineering such as
dissipation dilution and strain engineering, has been driven by human intuition
and insight. Such an approach is inefficient and leaves aside a plethora of
unexplored mechanical designs that potentially achieve better performance.
Here, we use a computer-aided inverse design approach known as topology
optimization to structurally design mechanical resonators with optimal
performance of the fundamental mechanical mode. Using the outcomes of this
approach, we fabricate and characterize ultra-coherent nanomechanical
resonators with record-high Qf products, entering a quantum coherent regime
where coherent oscillations are observed at room temperature. Further
refinements to the model describing the mechanical system are likely to improve
the Qf product even more. The proposed approach - which can be also used to
improve phononic crystal and coupled-mode resonators - opens up a new paradigm
for designing ultra-coherent micro- and nanomechanical resonators for
cutting-edge technology, enabling e.g. novel experiments in fundamental physics
(e.g. search for dark matter and quantum nature of gravity) and extreme sensing
of magnetic fields, electric fields and mass with unprecedented sensitivities
at room temperature
Ultrahigh finesse Fabry-Perot superconducting resonator
We have built a microwave Fabry-Perot resonator made of diamond-machined
copper mirrors coated with superconducting niobium. Its damping time (Tc = 130
ms at 51 GHz and 0.8 K) corresponds to a finesse of 4.6 x 109, the
highest ever reached for a Fabry-Perot in any frequency range. This result
opens novel perspectives for quantum information, decoherence and non-locality
studies
Quantum jumps of light recording the birth and death of a photon in a cavity
A microscopic system under continuous observation exhibits at random times
sudden jumps between its states. The detection of this essential quantum
feature requires a quantum non-demolition (QND) measurement repeated many times
during the system evolution. Quantum jumps of trapped massive particles
(electrons, ions or molecules) have been observed, which is not the case of the
jumps of light quanta. Usual photodetectors absorb light and are thus unable to
detect the same photon twice. They must be replaced by a transparent counter
'seeing' photons without destroying them3. Moreover, the light has to be stored
over a duration much longer than the QND detection time. We have fulfilled
these challenging conditions and observed photon number quantum jumps.
Microwave photons are stored in a superconducting cavity for times in the
second range. They are repeatedly probed by a stream of non-absorbing atoms. An
atom interferometer measures the atomic dipole phase shift induced by the
non-resonant cavity field, so that the final atom state reveals directly the
presence of a single photon in the cavity. Sequences of hundreds of atoms
highly correlated in the same state, are interrupted by sudden
state-switchings. These telegraphic signals record, for the first time, the
birth, life and death of individual photons. Applying a similar QND procedure
to mesoscopic fields with tens of photons opens new perspectives for the
exploration of the quantum to classical boundary