18 research outputs found
Introduction to Quantum Noise, Measurement and Amplification
The topic of quantum noise has become extremely timely due to the rise of
quantum information physics and the resulting interchange of ideas between the
condensed matter and AMO/quantum optics communities. This review gives a
pedagogical introduction to the physics of quantum noise and its connections to
quantum measurement and quantum amplification. After introducing quantum noise
spectra and methods for their detection, we describe the basics of weak
continuous measurements. Particular attention is given to treating the standard
quantum limit on linear amplifiers and position detectors using a general
linear-response framework. We show how this approach relates to the standard
Haus-Caves quantum limit for a bosonic amplifier known in quantum optics, and
illustrate its application for the case of electrical circuits, including
mesoscopic detectors and resonant cavity detectors.Comment: Substantial improvements over initial version; include supplemental
appendices
Quantum Theory of Cavity-Assisted Sideband Cooling of Mechanical Motion
We present a fully quantum theory describing the cooling of a cantilever
coupled via radiation pressure to an illuminated optical cavity. Applying the
quantum noise approach to the fluctuations of the radiation pressure force, we
derive the opto-mechanical cooling rate and the minimum achievable phonon
number. We find that reaching the quantum limit of arbitrarily small phonon
numbers requires going into the good cavity (resolved phonon sideband) regime
where the cavity linewidth is much smaller than the mechanical frequency and
the corresponding cavity detuning. This is in contrast to the common assumption
that the mechanical frequency and the cavity detuning should be comparable to
the cavity damping.Comment: 5 pages, 2 figure
Dynamical multistability in high-finesse micromechanical optical cavities
We analyze the nonlinear dynamics of a high-finesse optical cavity in which
one mirror is mounted on a flexible mechanical element. We find that this
system is governed by an array of dynamical attractors, which arise from
phase-locking between the mechanical oscillations of the mirror and the ringing
of the light intensity in the cavity. We describe an analytical approximation
to map out the diagram of attractors in parameter space, derive the slow
amplitude dynamics of the system, including thermally activated hopping between
different attractors, and suggest a scheme for exploiting the dynamical
multistability in the measurement of small displacements.Comment: 5 pages, 4 figure
The information about the state of a qubit gained by a weakly coupled detector
We analyze the information that one can learn about the state of a quantum
two-level system, i.e. a qubit, when probed weakly by a nearby detector. In
particular, we focus on the case when the qubit Hamiltonian and the qubit's
operator being probed by the detector do not commute. Because the qubit's state
keeps evolving while being probed and because the measurement data is mixed
with a detector-related background noise, one might expect the detector to fail
in this case. We show, however, that under suitable conditions and by proper
analysis of the measurement data useful information about the state of the
qubit can be extracted. It turns out that the measurement basis is
stochastically determined every time the experiment is repeated. We analyze in
detail the probability distributions that govern the choice of measurement
bases. We also analyze the information acquisition rate and show that it is
largely unaffected by the apparent conflict between the measurement and
intrinsic qubit dynamics. We discuss the relation between our analysis and the
stochastic master equation that describes the evolution of the qubit's state
under the influence of measurement and decoherence. In particular, we write
down a stochastic equation that encompasses the usual stochastic master
equation for the evolution of the qubit's density matrix and additionally
contains the measurement information that can be extracted from the observed
signal.Comment: 21 pages (two column), 8 figure
Radiation-pressure self-cooling of a micromirror in a cryogenic environment
We demonstrate radiation-pressure cavity-cooling of a mechanical mode of a
micromirror starting from cryogenic temperatures. To achieve that, a
high-finesse Fabry-Perot cavity (F\approx 2200) was actively stabilized inside
a continuous-flow 4He cryostat. We observed optical cooling of the fundamental
mode of a 50mu x 50 mu x 5.4 mu singly-clamped micromirror at \omega_m=3.5 MHz
from 35 K to approx. 290 mK. This corresponds to a thermal occupation factor of
\approx 1x10^4. The cooling performance is only limited by the mechanical
quality and by the optical finesse of the system. Heating effects, e.g. due to
absorption of photons in the micromirror, could not be observed. These results
represent a next step towards cavity-cooling a mechanical oscillator into its
quantum ground state
Application of Resonance Perturbation Theory to Dynamics of Magnetization in Spin Systems Interacting with Local and Collective Bosonic Reservoirs
We apply our recently developed resonance perturbation theory to describe the
dynamics of magnetization in paramagnetic spin systems interacting
simultaneously with local and collective bosonic environments. We derive
explicit expressions for the evolution of the reduced density matrix elements.
This allows us to calculate explicitly the dynamics of the macroscopic
magnetization, including characteristic relaxation and dephasing time-scales.
We demonstrate that collective effects (i) do not influence the character of
the relaxation processes but merely renormalize the relaxation times, and (ii)
significantly modify the dephasing times, leading in some cases to a
complicated (time inhomogeneous) dynamics of the transverse magnetization,
governed by an effective time-dependent magnetic field
Cavity cooling of a nanomechanical resonator by light scattering
We present a novel method for opto-mechanical cooling of sub-wavelength sized
nanomechanical resonators. Our scheme uses a high finesse Fabry-Perot cavity of
small mode volume, within which the nanoresonator is acting as a
position-dependant perturbation by scattering. In return, the back-action
induced by the cavity affects the nanoresonator dynamics and can cool its
fluctuations. We investigate such cavity cooling by scattering for a nanorod
structure and predict that ground-state cooling is within reach.Comment: 4 pages, 3 figure
Quantum nano-electromechanics with electrons, quasiparticles and Cooper pairs: effective bath descriptions and strong feedback effects
Using a quantum noise approach, we discuss the physics of both normal metal
and superconducting single electron transistors (SET) coupled to mechanical
resonators. Particular attention is paid to the regime where transport occurs
via incoherent Cooper-pair tunneling (either via the Josephson quasiparticle
(JQP) or double Josephson quasiparticle (DJQP) process). We show that,
surprisingly, the back-action of tunneling Cooper pairs (or superconducting
quasiparticles) can be used to significantly cool the oscillator. We also
discuss the physical origin of negative damping effects in this system, and how
they can lead to a regime of strong electro-mechanical feedback, where despite
a weak SET - oscillator coupling, the motion of the oscillator strongly effects
the tunneling of the Cooper pairs. We show that in this regime, the oscillator
is characterized by an energy-dependent effective temperature. Finally, we
discuss the strong analogy between back-action effects of incoherent
Cooper-pair tunneling and ponderomotive effects in an optical cavity with a
moveable mirror; in our case, tunneling Cooper pairs play the role of the
cavity photons.Comment: 27 pages, 7 figures; submitted to the New Journal of Physics focus
issue on Nano-electromechanical Systems; error in references correcte
Circuit Quantum Electrodynamics: Coherent Coupling of a Single Photon to a Cooper Pair Box
Under appropriate conditions, superconducting electronic circuits behave
quantum mechanically, with properties that can be designed and controlled at
will. We have realized an experiment in which a superconducting two-level
system, playing the role of an artificial atom, is strongly coupled to a single
photon stored in an on-chip cavity. We show that the atom-photon coupling in
this circuit can be made strong enough for coherent effects to dominate over
dissipation, even in a solid state environment. This new regime of matter light
interaction in a circuit can be exploited for quantum information processing
and quantum communication. It may also lead to new approaches for single photon
generation and detection.Comment: 8 pages, 4 figures, accepted for publication in Nature, embargo does
apply, version with high resolution figures available at:
http://www.eng.yale.edu/rslab/Andreas/content/science/PubsPapers.htm
Phase preserving amplification near the quantum limit with a Josephson Ring Modulator
Recent progress in solid state quantum information processing has stimulated
the search for ultra-low-noise amplifiers and frequency converters in the
microwave frequency range, which could attain the ultimate limit imposed by
quantum mechanics. In this article, we report the first realization of an
intrinsically phase-preserving, non-degenerate superconducting parametric
amplifier, a so far missing component. It is based on the Josephson ring
modulator, which consists of four junctions in a Wheatstone bridge
configuration. The device symmetry greatly enhances the purity of the
amplification process and simplifies both its operation and analysis. The
measured characteristics of the amplifier in terms of gain and bandwidth are in
good agreement with analytical predictions. Using a newly developed noise
source, we also show that our device operates within a factor of three of the
quantum limit. This development opens new applications in the area of quantum
analog signal processing