16 research outputs found

### Effects of Entanglement in Controlled Dephasing

In controlled dephasing as a result of the interaction of a controlled
environment (dephasor) and the system under observation (dephasee) the states
of the two subsystems are entangled. Using as an example the ``Which Path
Detector'', we discuss how the entanglement influences the controlled
dephasing. In particular, we calculate the suppression $\nu$ of A-B
oscillations as a function of the bias $eV$ applied to the QPC and the coupling
$\Gamma$ of the QD to the leads. At low temperatures the entanglement produces
a smooth crossover from $\nu \propto (eV/\Gamma)^2$, when $eV \ll \Gamma$ to
$\nu \propto eV/\Gamma$, for $eV \gg \Gamma$.Comment: 4 pages, 1 figur

### Quantum Mechanics Lecture Notes. Selected Chapters

These are extended lecture notes of the quantum mechanics course which I am
teaching in the Weizmann Institute of Science graduate physics program. They
cover the topics listed below. The first four chapter are posted here. Their
content is detailed on the next page. The other chapters are planned to be
added in the coming months.
1. Motion in External Electromagnetic Field. Gauge Fields in Quantum
Mechanics.
2. Quantum Mechanics of Electromagnetic Field
3. Photon-Matter Interactions
4. Quantization of the Schr\"odinger Field (The Second Quantization)
5. Open Systems. Density Matrix
6. Adiabatic Theory. The Berry Phase. The Born-Oppenheimer Approximation
7. Mean Field Approaches for Many Body Systems -- Fermions and Boson

### Semiconductor Microstructure in a Squeezed Vacuum: Electron-Hole Plasma Luminescence

We consider a semiconductor quantum-well placed in a wave guide microcavity
and interacting with the broadband squeezed vacuum radiation, which fills one
mode of the wave guide with a large average occupation. The wave guide modifies
the optical density of states so that the quantum well interacts mostly with
the squeezed vacuum. The vacuum is squeezed around the externally controlled
central frequency \om_0, which is tuned above the electron-hole gap $E_g$,
and induces fluctuations in the interband polarization of the quantum-well. The
power spectrum of scattered light exhibits a peak around \om_0, which is
moreover non-Lorentzian and is a result of both the squeezing and the
particle-hole continuum. The squeezing spectrum is qualitatively different from
the atomic case. We discuss the possibility to observe the above phenomena in
the presence of additional non-radiative (e-e, phonon) dephasing.Comment: 6 pages, 3 figure

### Atom in a coherently controlled squeezed vacuum

A broadband squeezed vacuum photon field is characterized by a complex
squeezing function. We show that by controlling the wavelength dependence of
its phase it is possible to change the dynamics of the atomic polarization
interacting with the squeezed vacuum. Such a phase modulation effectively
produces a finite range temporal interaction kernel between the two quadratures
of the atomic polarization yielding the change in the decay rates as well as
the appearance of additional oscillation frequencies. We show that decay rates
slower than the spontaneous decay rate can be achieved even for a squeezed bath
in the classic regime. For linear and quadratic phase modulations the power
spectrum of the scattered light exhibits narrowing of the central peak due to
the modified decay rates. For strong phase modulations side lobes appear
symmetrically around the central peak reflecting additional oscillation
frequencies.Comment: 4 pages, 4 figure

### Coherent optical control of correlation waves of spins in semiconductors

We calculate the dynamical fluctuation spectrum of electronic spins in a
semiconductor under a steady-state illumination by light containing
polarization squeezing correlations. Taking into account quasi-particle
lifetime and spin relaxation for this non-equilibrium situation we consider up
to fourth order optical effects which are sensitive to the squeezing phases.
We demonstrate the possibility to control the spin fluctuations by optically
modulating these phases as a function of frequency, leading to a non-Lorentzian
spectrum which is very different from the thermal equilibrium fluctuations in
n-doped semiconductors. Specifically, in the time-domain spin-spin correlation
can exhibit time delays and sign flips originating from the phase modulations
and correlations of polarizations, respectively. For higher light intensity we
expect a regime where the squeezing correlations will dominate the spectrum.Comment: 17 pages, 8 figure

### Qubit Coherent Control with Squeezed Light Fields

We study the use of squeezed light for qubit coherent control and compare it
with the coherent state control field case. We calculate the entanglement
between a short pulse of resonant squeezed light and a two-level atom in free
space and the resulting operation error. We find that the squeezing phase, the
phase of the light field and the atomic superposition phase, all determine
whether atom-pulse mode entanglement and the gate error are enhanced or
suppressed. However, when averaged over all possible qubit initial states, the
gate error would not decrease by a practicably useful amount and would in fact
increase in most cases. We discuss the possibility of measuring the increased
gate error as a signature of the enhancement of entanglement by squeezing.Comment: 12 pages, 6 figure