105 research outputs found
Coherent spectroscopy of rare-earth-ion doped whispering-gallery mode resonators
We perform an investigation into the properties of Pr3+:Y2SiO5 whispering
gallery mode resonators as a first step towards achieving the strong coupling
regime of cavity QED with rare-earth-ion doped crystals. Direct measurement of
cavity QED parameters are made using photon echoes, giving good agreement with
theoretical predictions. By comparing the ions at the surface of the resonator
to those in the center it is determined that the physical process of making the
resonator does not negatively affect the properties of the ions. Coupling
between the ions and resonator is analyzed through the observation of optical
bistability and normal-mode splitting.Comment: 8 pages, 9 figure
Laser cooling and control of excitations in superfluid helium
Superfluidity is an emergent quantum phenomenon which arises due to strong
interactions between elementary excitations in liquid helium. These excitations
have been probed with great success using techniques such as neutron and light
scattering. However measurements to-date have been limited, quite generally, to
average properties of bulk superfluid or the driven response far out of thermal
equilibrium. Here, we use cavity optomechanics to probe the thermodynamics of
superfluid excitations in real-time. Furthermore, strong light-matter
interactions allow both laser cooling and amplification of the thermal motion.
This provides a new tool to understand and control the microscopic behaviour of
superfluids, including phonon-phonon interactions, quantised vortices and
two-dimensional quantum phenomena such as the Berezinskii-Kosterlitz-Thouless
transition. The third sound modes studied here also offer a pathway towards
quantum optomechanics with thin superfluid films, including femtogram effective
masses, high mechanical quality factors, strong phonon-phonon and phonon-vortex
interactions, and self-assembly into complex geometries with sub-nanometre
feature size.Comment: 6 pages, 4 figures. Supplementary information attache
Microphotonic Forces From Superfluid Flow
In cavity optomechanics, radiation pressure and photothermal forces are
widely utilized to cool and control micromechanical motion, with applications
ranging from precision sensing and quantum information to fundamental science.
Here, we realize an alternative approach to optical forcing based on superfluid
flow and evaporation in response to optical heating. We demonstrate optical
forcing of the motion of a cryogenic microtoroidal resonator at a level of 1.46
nN, roughly one order of magnitude larger than the radiation pressure force. We
use this force to feedback cool the motion of a microtoroid mechanical mode to
137 mK. The photoconvective forces demonstrated here provide a new tool for
high bandwidth control of mechanical motion in cryogenic conditions, and have
the potential to allow efficient transfer of electromagnetic energy to motional
kinetic energy.Comment: 5 pages, 6 figure
Photon echo quantum memories in inhomogeneously broadened two level atoms
Here we propose a solid-state quantum memory that does not require spectral
holeburning, instead using strong rephasing pulses like traditional photon echo
techniques. The memory uses external broadening fields to reduce the optical
depth and so switch off the collective atom-light interaction when desired. The
proposed memory should allow operation with reasonable efficiency in a much
broader range of material systems, for instance Er3+ doped crystals which have
a transition at 1.5 um. We present analytic theory supported by numerical
calculations and initial experiments.Comment: 7 pages, 8 figure
Strong coupling cavity QED using rare-earth-ion dopants in monolithic resonators: what you can do with a weak oscillator
We investigate the possibility of achieving the strong coupling regime of
cavity quantum electrodynamics using rare earth ions as impurities in
monolithic optical resonators. We conclude that due to the weak oscillator
strengths of the rare earths, it may be possible but difficult, to reach the
regime where the single photon Rabi frequency is large compared to both the
cavity and atom decay rates. However reaching the regime where the saturation
photon and atom numbers are less than one should be much more achievable. We
show that in this `bad cavity' regime, transfer of quantum states and an
optical phase shift conditional on the state of the atom is still possible, and
suggest a method for coherent detection of single dopants.Comment: 10 pages, 6 figure
Precision measurement of electronic ion-ion interactions between neighboring Eu3+ optical centers
We report measurements of discrete excitation-induced frequency shifts on the 7F0â5D0 transition of the Eu+ center in La:Lu:EuCl3·6D2O resulting from the optical excitation of neighboring Eu3+ ions. Shifts of up to 46.081±0.005ââMHz were observed. The magnitude of the interaction between neighboring ions was found to be significantly larger than expected from the electric dipole-dipole mechanism often observed in rare earth systems. We show that a large network of interacting and individually addressable centers can be created by lightly doping crystals otherwise stoichiometric in the optically active rare earth ion, and that this network could be used to implement a quantum processor with more than ten qubits
Reducing decoherence in optical and spin transitions in rare-earth-ion doped materials
In many important situations the dominant dephasing mechanism in cryogenic
rare-earth-ion doped systems is due to magnetic field fluctuations from spins
in the host crystal. Operating at a magnetic field where a transition has a
zero first-order-Zeeman (ZEFOZ) shift can greatly reduce this dephasing. Here
we identify the location of transitions with zero first-order Zeeman shift for
optical transitions in Pr3+:YAG and for spin transitions in Er3+:Y2SiO5. The
long coherence times that ZEFOZ would enable would make Pr3+:YAG a strong
candidate for achieving the strong coupling regime of cavity QED, and would be
an important step forward in creating long-lived telecommunications wavelength
quantum memories in Er3+:Y2SiO5. This work relies mostly on published spin
Hamiltonian parameters but Raman heterodyne spectroscopy was performed on
Pr3+:YAG to measure the parameters for the excited state.Comment: 10 pages, 5 figure
The first legal mortgagor: a consumer without adequate protection?
This article contends that the UK governmentâs attempt to create a well-functioning consumer credit market will be undermined if it fails to reform the private law framework relating to the first legal mortgage. Such agreements are governed by two distinct regulatory regimes that are founded upon very different conceptions of the mortgagor. The first, the regulation of financial services overseen by the Financial Conduct Authority, derives from public law and is founded upon a conception of the mortgagor as âconsumerâ. The other is land law, private law regulation implemented by the judiciary and underpinned by a conception of the mortgagor as âlandownerâ. Evidence suggests that the operation of these two regimes prevents mortgagors from receiving fair and consistent treatment. The current reform of financial services regulation therefore will change only one part of this governance regime and will leave mortgagors heavily reliant upon a regulator that still has to prove itself. What this article argues is that reform of the rules of private law must also be undertaken with the aim of initiating a paradigm shift in the conception of the mortgagor from âlandownerâ to âconsumerâ. Cultural shifts of this kind take time but the hope is that this conceptual transformation will occur in time to deter the predicted rise in mortgage possessions
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