17 research outputs found
Gravitationally-induced entanglement in cold atoms
A promising route to testing quantum gravity in the laboratory is to look for
gravitationally-induced entanglement (GIE) between two or more quantum matter
systems. Proposals for such tests have principally used microsolid systems,
with highly non-classical states, such as N00N states or highly-squeezed
states. Here, we consider, for the first time, GIE between two atomic gas
interferometers as a test of quantum gravity. We propose placing the two
interferometers next to each other in parallel and looking for correlations in
the number of atoms at the output ports as evidence of GIE and quantum gravity.
GIE is possible without challenging macroscopic superposition states, such as
N00N or Schr\"odinger cat states, and instead there can be just classical-like
'coherent' states of atoms. This requires the total mass of the atom
interferometers to be on the Planck mass scale, and long integration times.
However, with current state-of-the-art quantum squeezing in cold atoms, we
argue that the mass scale can be reduced to approachable levels and detail how
such a mass scale can be achieved in the near future.Comment: 14 pages, 3 figure
Dual-frequency Doppler-free spectroscopy for compact atomic physics experiments
Vapour-cell spectroscopy is widely used for the frequency stabilisation of
diode lasers relative to specific atomic transitions - a technique essential in
cold atom and ion trapping experiments. Two laser beams, tuned to different
frequencies, can be overlapped on the same spatial path as an aid to
compactness; this method also enhances the resulting spectroscopic signal via
optical pumping effects, yielding an increase in the sensitivity of
spectroscopically-generated laser stabilisation signals. Doppler-free locking
features become visible over a frequency range several hundred MHz wider than
for standard saturated absorption spectroscopy. Herein we present the measured
Doppler-free spectroscopy signals from an atomic vapour cell as a function of
both laser frequencies, showing experimental data that covers the full, 2D
parameter space associated with dual-frequency spectroscopy. We consider how
dual-frequency spectroscopy could be used for enhanced frequency-stabilisation
of one laser, or alternatively to frequency-stabilise two lasers
simultaneously, and analyse the likely performance of such stabilisation
methods based on our experimental results. We discuss the underlying physical
mechanism of the technique and show that a simple rate-equation model
successfully predicts the key qualitative features of our resultsComment: 12 pages, 5 figure
Influence of molecular temperature on the coherence of fullerenes in a near-field interferometer
We study C70 fullerene matter waves in a Talbot-Lau interferometer as a
function of their temperature. While the ideal fringe visibility is observed at
moderate molecular temperatures, we find a gradual degradation of the
interference contrast if the molecules are heated before entering the
interferometer. A method is developed to assess the distribution of the
micro-canonical temperatures of the molecules in free flight. This way the
heating-dependent reduction of interference contrast can be compared with the
predictions of quantum theory. We find that the observed loss of coherence
agrees quantitatively with the expected decoherence rate due to the thermal
radiation emitted by the hot molecules.Comment: 11 pages, 9 figure
Enhanced magnetoassociation of Li in the quantum degenerate regime
We study magnetic Feshbach resonance of ultracold Li atoms in a dipole
trap close to quantum degeneracy. The experiment is carried out by linearly
ramping down the magnetic field from the BCS to the BEC side around the broad
resonance at G. The Feshbach molecule formation efficiency depends
strongly on the temperature of the atomic gas and the rate at which the
magnetic field is ramped across the Feshbach resonance. The molecular
association process is well described by the Landau-Zener transition while
above the Fermi temperature, such that two-body physics dominates the dynamics.
However, we observe an enhancement of the atom-molecule coupling as the
Fermionic atoms reach degeneracy, demonstrating the importance of many-body
coherence not captured by the conventional Landau-Zener model. We develop a
theoretical model that explains the temperature dependence of the atom-molecule
coupling. Furthermore, we characterize this dependence experimentally and
extract the atom-molecule coupling coefficient as a function of temperature,
finding qualitative agreement between our model and experimental results.
Accurate measurement of this coupling coefficient is important for both
theoretical and experimental studies of atom-molecule association dynamics.Comment: 6 pages, 4 figure
Collisional decoherence observed in matter wave interferometry
We study the loss of spatial coherence in the extended wave function of
fullerenes due to collisions with background gases. From the gradual
suppression of quantum interference with increasing gas pressure we are able to
support quantitatively both the predictions of decoherence theory and our
picture of the interaction process. We thus explore the practical limits of
matter wave interferometry at finite gas pressures and estimate the required
experimental vacuum conditions for interferometry with even larger objects.Comment: 4 pages, 3 figure
The wave nature of biomolecules and fluorofullerenes
We demonstrate quantum interference for tetraphenylporphyrin, the first
biomolecule exhibiting wave nature, and for the fluorofullerene C60F48 using a
near-field Talbot-Lau interferometer. For the porphyrins, which are
distinguished by their low symmetry and their abundant occurence in organic
systems, we find the theoretically expected maximal interference contrast and
its expected dependence on the de Broglie wavelength. For C60F48 the observed
fringe visibility is below the expected value, but the high contrast still
provides good evidence for the quantum character of the observed fringe
pattern. The fluorofullerenes therefore set the new mark in complexity and mass
(1632 amu) for de Broglie wave experiments, exceeding the previous mass record
by a factor of two.Comment: 5 pages, 4 figure
Decoherence of matter waves by thermal emission of radiation
Emergent quantum technologies have led to increasing interest in decoherence
- the processes that limit the appearance of quantum effects and turn them into
classical phenomena. One important cause of decoherence is the interaction of a
quantum system with its environment, which 'entangles' the two and distributes
the quantum coherence over so many degrees of freedom as to render it
unobservable. Decoherence theory has been complemented by experiments using
matter waves coupled to external photons or molecules, and by investigations
using coherent photon states, trapped ions and electron interferometers. Large
molecules are particularly suitable for the investigation of the
quantum-classical transition because they can store much energy in numerous
internal degrees of freedom; the internal energy can be converted into thermal
radiation and thus induce decoherence. Here we report matter wave
interferometer experiments in which C70 molecules lose their quantum behaviour
by thermal emission of radiation. We find good quantitative agreement between
our experimental observations and microscopic decoherence theory. Decoherence
by emission of thermal radiation is a general mechanism that should be relevant
to all macroscopic bodies.Comment: 5 pages, 4 figure
Quantum decoherence of phonons in Bose–Einstein condensates
We apply modern techniques from quantum optics and quantum information science to Bose–Einstein condensates(BECs)in order to study, for the first time, the quantum decoherence of phonons of isolated BECs. In the last few years, major advances in the manipulation and control of phonons have highlighted their potential as carriers of quantum information in quantum technologies, particularly in quantum processing and quantum communication. Although most of these studies have focused on trapped ion and crystalline systems, another promising system that has remained relatively unexplored is BECs. The potential benefits in using this system have been emphasized recently with proposals of relativistic quantum devices that exploit quantum states of phonons in BECs to achieve, in principle, superior performance over standard non-relativistic devices. Quantum decoherence is often the limiting factor in the practical realization of quantum technologies, but here we show that quantum decoherence of phonons is not expected to heavily constrain the performance of these proposed relativistic quantum devices