49 research outputs found
Two-Tone Optomechanical Instability and Its Fundamental Implications for Backaction-Evading Measurements
While quantum mechanics imposes a fundamental limit on the precision of
interferometric measurements of mechanical motion due to measurement
backaction, the nonlinear nature of the coupling also leads to parametric
instabilities that place practical limits on the sensitivity by limiting the
power in the interferometer. Such instabilities have been extensively studied
in the context of gravitational wave detectors, and their presence has recently
been reported in Advanced LIGO. Here, we observe experimentally and describe
theoretically a new type of optomechanical instability that arises in two-tone
backaction-evading (BAE) measurements, designed to overcome the standard
quantum limit, and demonstrate the effect in the optical domain with a photonic
crystal nanobeam, and in the microwave domain with a micromechanical oscillator
coupled to a microwave resonator. In contrast to the well-known oscillatory
parametric instability that occurs in single-tone, blue-detuned pumping, which
is characterized by a vanishing effective mechanical damping, the parametric
instability in balanced two-tone optomechanics is exponential, and is a result
of small detuning errors in the two pump frequencies. Its origin can be
understood in a rotating frame as the vanishing of the effective mechanical
frequency due to an optical spring effect. Counterintuitively, the instability
occurs even in the presence of perfectly balanced intracavity fields, and can
occur for both signs of detuning. We find excellent quantitative agreement with
our theoretical predictions. Since the constraints on tuning accuracy become
stricter with increasing probe power, it imposes a fundamental limitation on
BAE measurements, as well as other two-tone schemes. In addition to introducing
a new limitation in two-tone BAE measurements, the results also introduce a new
type of nonlinear dynamics in cavity optomechanics
Weak-Values Technique for Velocity Measurements
In a recent Letter, Brunner and Simon proposed an interferometric scheme using imaginary weak values with a frequency-domain analysis to outperform standard interferometry in longitudinal phase shifts [Phys. Rev. Lett 105, 010405 (2010)]. Here we demonstrate an interferometric scheme combined with a time-domain analysis to measure longitudinal velocities. The technique employs the near-destructive interference of non-Fourier limited pulses, one Doppler shifted due to a moving mirror in a Michelson interferometer. We achieve a velocity measurement of 400ââfm/s and show our estimator to be efficient by reaching its CramĂ©râRao bound
Experimental investigation of the transition between Autler-Townes splitting and electromagnetically-induced-transparency models
Two phenomena can affect the transmission of a probe field through an absorbing medium in the presence of an additional field: electromagnetically induced transparency (EIT) and Autler-Townes splitting (ATS). Being able to discriminate between the two i
Spontaneous creation of Kibble-Zurek solitons in a Bose-Einstein condensate
When a system crosses a second-order phase transition on a finite timescale,
spontaneous symmetry breaking can cause the development of domains with
independent order parameters, which then grow and approach each other creating
boundary defects. This is known as Kibble-Zurek mechanism. Originally
introduced in cosmology, it applies both to classical and quantum phase
transitions, in a wide variety of physical systems. Here we report on the
spontaneous creation of solitons in Bose-Einstein condensates via the
Kibble-Zurek mechanism. We measure the power-law dependence of defects number
with the quench time, and provide a check of the Kibble-Zurek scaling with the
sonic horizon. These results provide a promising test bed for the determination
of critical exponents in Bose-Einstein condensates.Comment: 7 pages, 4 figure
From Coherent Modes to Turbulence and Granulation of Trapped Gases
The process of exciting the gas of trapped bosons from an equilibrium initial
state to strongly nonequilibrium states is described as a procedure of symmetry
restoration caused by external perturbations. Initially, the trapped gas is
cooled down to such low temperatures, when practically all atoms are in
Bose-Einstein condensed state, which implies the broken global gauge symmetry.
Excitations are realized either by imposing external alternating fields,
modulating the trapping potential and shaking the cloud of trapped atoms, or it
can be done by varying atomic interactions by means of Feshbach resonance
techniques. Gradually increasing the amount of energy pumped into the system,
which is realized either by strengthening the modulation amplitude or by
increasing the excitation time, produces a series of nonequilibrium states,
with the growing fraction of atoms for which the gauge symmetry is restored. In
this way, the initial equilibrium system, with the broken gauge symmetry and
all atoms condensed, can be excited to the state, where all atoms are in the
normal state, with completely restored gauge symmetry. In this process, the
system, starting from the regular superfluid state, passes through the states
of vortex superfluid, turbulent superfluid, heterophase granular fluid, to the
state of normal chaotic fluid in turbulent regime. Both theoretical and
experimental studies are presented.Comment: Latex file, 25 pages, 4 figure
Nonlinearity and Topology
The interplay of nonlinearity and topology results in many novel and emergent
properties across a number of physical systems such as chiral magnets, nematic
liquid crystals, Bose-Einstein condensates, photonics, high energy physics,
etc. It also results in a wide variety of topological defects such as solitons,
vortices, skyrmions, merons, hopfions, monopoles to name just a few.
Interaction among and collision of these nontrivial defects itself is a topic
of great interest. Curvature and underlying geometry also affect the shape,
interaction and behavior of these defects. Such properties can be studied using
techniques such as, e.g. the Bogomolnyi decomposition. Some applications of
this interplay, e.g. in nonreciprocal photonics as well as topological
materials such as Dirac and Weyl semimetals, are also elucidated
Simulating the vibrational quantum dynamics of molecules using photonics
Advances in control techniques for vibrational quantum states in molecules present new challenges for modelling such systems, which could be amenable to quantum simulation methods. Here, by exploiting a natural mapping between vibrations in molecules and photons in waveguides, we demonstrate a reprogrammable photonic chip as a versatile simulation platform for a range of quantum dynamic behaviour in different molecules. We begin by simulating the time evolution of vibrational excitations in the harmonic approximation for several four-atom molecules, including H2CS, SO3, HNCO, HFHF, N4 and P4. We then simulate coherent and dephased energy transport in the simplest model of the peptide bond in proteinsâN-methylacetamideâand simulate thermal relaxation and the effect of anharmonicities in H2O. Finally, we use multi-photon statistics with a feedback control algorithm to iteratively identify quantum states that increase a particular dissociation pathway of NH3. These methods point to powerful new simulation tools for molecular quantum dynamics and the field of femtochemistry
Floquet dynamics in the quantum measurement of mechanical motion
The radiation-pressure interaction between one or more laser fields and a
mechanical oscillator gives rise to a wide range of phenomena: from sideband
cooling and backaction-evading measurements to pondermotive and mechanical
squeezing to entanglement and motional sideband asymmetry. In many protocols,
such as dissipative mechanical squeezing, multiple lasers are utilized, giving
rise to periodically driven optomechanical systems. Here we show that in this
case, Floquet dynamics can arise due to presence of Kerr-type nonlinearities,
which are ubiqitious in optomechanical systems. Specifically, employing
multiple probe tones, we perform sideband asymmetry measurements, a macroscopic
quantum effect, on a silicon optomechanical crystal sideband-cooled to 40%
ground-state occupation. We show that the Floquet dynamics, resulting from the
presence of multiple pump tones, gives rise to an artificially modified
motional sideband asymmetry by redistributing thermal and quantum fluctuations
among the initially independently scattered thermomechanical sidebands. For
pump tones exhibiting large frequency separation, the dynamics is suppressed
and accurate quantum noise thermometry demonstrated. We develop a theoretical
model based on Floquet theory that accurately describes our observations. The
resulting dynamics can be understood as resulting from a synthetic gauge field
among the Fourier modes, which is created by the phase lag of the Kerr-type
response. This novel phenomenon has wide-ranging implications for schemes
utilizing several pumping tones, as commonly employed in backaction-evading
measurements, dissipative optical squeezing, dissipative mechanical squeezing
and quantum noise thermometry. Our observation may equally well be used for
optomechanical Floquet engineering, e.g. generation of topological phases of
sound by periodic time-modulation
Experimental investigation of the transition between Autler-Townes splitting and electromagnetically-induced transparency models
Paper IA_6_2 - From the session Coherent Effects (IA_6)If in general the transparency of an initially absorbing medium for a probe field is increased by the presence of a control field on an adjacent transition, two very different processes can be invoked to explain it. One of them is a quantum Fano interference between two paths in the three-level system, which occurs even at low control intensity and gives rise to electromagnetically-induced transparency (EIT), the other one is the appearance of two dressed states in the excited level at higher control intensity, corresponding to the Autler-Townes splitting (ATS). This distinction is particularly critical for instance for the implementation of slow light or optical quantum memories. In a recent paper, P. M. Anisimov, J. P. Dowling and B. C. Sanders proposed a quantitative test to objectively discerning ATS from EIT [1]. We experimentally investigated this test with cold atoms [2] and demonstrated that it is very sensitive to the specific properties of the medium. © 2013 IEEE.L. Giner, L. Veissier, B. Sparkes, A. Sheremet, A. Nicolas, O. Mishina, M. Scherman, S. Burks, I. Shomroni, D. V. Kupriyanov, P. K. Lam, E. Giacobino, J. Laura