3,147 research outputs found
The interpretation of non-Markovian stochastic Schr\"odinger equations as a hidden-variable theory
Do diffusive non-Markovian stochastic Schr\"odinger equations (SSEs) for open
quantum systems have a physical interpretation? In a recent paper [Phys. Rev. A
66, 012108 (2002)] we investigated this question using the orthodox
interpretation of quantum mechanics. We found that the solution of a
non-Markovian SSE represents the state the system would be in at that time if a
measurement was performed on the environment at that time, and yielded a
particular result. However, the linking of solutions at different times to make
a trajectory is, we concluded, a fiction. In this paper we investigate this
question using the modal (hidden variable) interpretation of quantum mechanics.
We find that the noise function appearing in the non-Markovian SSE can
be interpreted as a hidden variable for the environment. That is, some chosen
property (beable) of the environment has a definite value even in the
absence of measurement on the environment. The non-Markovian SSE gives the
evolution of the state of the system ``conditioned'' on this environment hidden
variable. We present the theory for diffusive non-Markovian SSEs that have as
their Markovian limit SSEs corresponding to homodyne and heterodyne detection,
as well as one which has no Markovian limit.Comment: 9 page
Gas fluidized bed polymerization.
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Improved qubit bifurcation readout in the straddling regime of circuit QED
We study bifurcation measurement of a multi-level superconducting qubit using
a nonlinear resonator biased in the straddling regime, where the resonator
frequency sits between two qubit transition frequencies. We find that
high-fidelity bifurcation measurements are possible because of the enhanced
qubit-state-dependent pull of the resonator frequency, the behavior of
qubit-induced nonlinearities and the reduced Purcell decay rate of the qubit
that can be realized in this regime. Numerical simulations find up to a
threefold improvement in qubit readout fidelity when operating in, rather than
outside of, the straddling regime. High-fidelity measurements can be obtained
at much smaller qubit-resonator couplings than current typical experimental
realizations, reducing spectral crowding and potentially simplifying the
implementation of multi-qubit devices.Comment: 9 pages, 6 figure
High-resolution mid-infrared spectroscopy based on ultrafast Cr:ZnSe laser
High-resolution broadband direct frequency comb spectroscopy in the mid-infrared spectral region is an extremely powerful and versatile experimental technique that allows study of the molecular structure of gaseous compounds with multiple applicative and scientific implications. Here we present the first implementation of an ultrafast Cr:ZnSe mode-locked laser covering more than 7 THz at around the emission wavelength of 2.4 um, for direct frequency comb molecular spectroscopy with a frequency sampling of 220 MHz and a frequency resolution of 100 kHz. This technique is based on a scanning micro-cavity resonator with a Finesse of 12,000 and a diffraction reflecting grating. We demonstrate its application in high-precision spectroscopy of the acetylene molecule by retrieving line center frequencies of more than 68 roto-vibrational lines. Our technique paves the way for real time spectroscopic studies as well as for hyperspectral imaging techniques
Quantum trajectory approach to circuit QED: Quantum jumps and the Zeno effect
We present a theoretical study of a superconducting charge qubit dispersively
coupled to a transmission line resonator. Starting from a master equation
description of this coupled system and using a polaron transformation, we
obtain an exact effective master equation for the qubit. We then use quantum
trajectory theory to investigate the measurement of the qubit by continuous
homodyne measurement of the resonator out-field. Using the same porlaron
transformation, a stochastic master equation for the conditional state of the
qubit is obtained. From this result, various definitions of the measurement
time are studied. Furthermore, we find that in the limit of strong homodyne
measurement, typical quantum trajectories for the qubit exhibit a crossover
from diffusive to jump-like behavior. Finally, in the presence of Rabi drive on
the qubit, the qubit dynamics is shown to exhibit quantum Zeno behavior.Comment: 20 pages, 12 figure
Mid-infrared frequency comb spanning an octave based on an Er fiber laser and difference-frequency generation
We describe a coherent mid-infrared continuum source with 700 cm-1 usable
bandwidth, readily tuned within 600 - 2500 cm-1 (4 - 17 \mum) and thus covering
much of the infrared "fingerprint" molecular vibration region. It is based on
nonlinear frequency conversion in GaSe using a compact commercial 100-fs-pulsed
Er fiber laser system providing two amplified near-infrared beams, one of them
broadened by a nonlinear optical fiber. The resulting collimated mid-infrared
continuum beam of 1 mW quasi-cw power represents a coherent infrared frequency
comb with zero carrier-envelope phase, containing about 500,000 modes that are
exact multiples of the pulse repetition rate of 40 MHz. The beam's
diffraction-limited performance enables long-distance spectroscopic probing as
well as maximal focusability for classical and ultraresolving near-field
microscopies. Applications are foreseen also in studies of transient chemical
phenomena even at ultrafast pump-probe scale, and in high-resolution gas
spectroscopy for e.g. breath analysis.Comment: 8 pages, 2 figures revised version, added reference
Stochastic Schroedinger Equations with General Complex Gaussian Noises
Within the framework of stochastic Schroedinger equations, we show that the
correspondence between statevector equations and ensemble equations is
infinitely many to one, and we discuss the consequences. We also generalize the
results of [Phys. Lett. A 224, p. 25 (1996)] to the case of more general
complex Gaussian noises and analyze the two important cases of purely real and
purely imaginary stochastic processes.Comment: 5 pages, LaTeX. To appear on Phys. Rev.
Optimal generation of Fock states in a weakly nonlinear oscillator
We apply optimal control theory to determine the shortest time in which an
energy eigenstate of a weakly anharmonic oscillator can be created under the
practical constraint of linear driving. We show that the optimal pulses are
beatings of mostly the transition frequencies for the transitions up to the
desired state and the next leakage level. The time of a shortest possible pulse
for a given nonlinearity scale with the nonlinearity parameter delta as a power
law of alpha with alpha=-0.73 +/-0.029. This is a qualitative improvement
relative to the value alpha=1 suggested by a simple Landau-Zener argument.Comment: 10 pages, 6 figure
Beyond locutionary denotations: exploring trust between practitioners and policy
This study reports the findings of a research on the trust relationship between practitioners in the Skills for Life (SfL) area and the policy that informs their practice. The exploration of this relationship was premised on an extended notion of trust relationship which draws from the Speech Act theory of Austin (1962; Searle 1969; Kissine 2008), leading to the claim that the existence of different layers of imports in textual analysis makes it possible for a trust relationship to exist between the human/physical and the non human/non physical. The study found that the majority of practitioners in the SfL field trust policy to deliver its inherent policy only to a limited extent. Amongst others, the study identified the impact of the perlocutionary import of policy text on practitioners as a viable reason for this limited level of trust. Such perlocutionary imports, it also found, have adverse impact on practitioners who are considered to have drawn from previous experience to mediate the import of contemporary policies
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