831 research outputs found
Macroscopic quantum jumps and entangled state preparation
Recently we predicted a random blinking, i.e. macroscopic quantum jumps, in
the fluorescence of a laser-driven atom-cavity system [Metz et al., Phys. Rev.
Lett. 97, 040503 (2006)]. Here we analyse the dynamics underlying this effect
in detail and show its robustness against parameter fluctuations. Whenever the
fluorescence of the system stops, a macroscopic dark period occurs and the
atoms are shelved in a maximally entangled ground state. The described setup
can therefore be used for the controlled generation of entanglement. Finite
photon detector efficiencies do not affect the success rate of the state
preparation, which is triggered upon the observation of a macroscopic
fluorescence signal. High fidelities can be achieved even in the vicinity of
the bad cavity limit due to the inherent role of dissipation in the jump
process.Comment: 14 pages, 12 figures, proof of the robustness of the state
preparation against parameter fluctuations added, figure replace
Robust Entanglement through Macroscopic Quantum Jumps
We propose an entanglement generation scheme that requires neither the
coherent evolution of a quantum system nor the detection of single photons.
Instead, the desired state is heralded by a {\em macroscopic} quantum jump.
Macroscopic quantum jumps manifest themselves as a random telegraph signal with
long intervals of intense fluorescence (light periods) interrupted by the
complete absence of photons (dark periods). Here we show that a system of two
atoms trapped inside an optical cavity can be designed such that a dark period
prepares the atoms in a maximally entangled ground state. Achieving fidelities
above 0.9 is possible even when the single-atom cooperativity parameter C is as
low as 10 and when using a photon detector with an efficiency as low as eta =
0.2.Comment: 5 pages, 4 figures, more detailed discussion of underlying physical
effect, references update
Measurement of the hyperfine structure of the S1/2-D5/2 transition in 43Ca+
The hyperfine structure of the S1/2-D5/2 quadrupole transition at 729 nm in
43Ca+ has been investigated by laser spectroscopy using a single trapped 43Ca+
ion. We determine the hyperfine structure constants of the metastable level as
A=-3.8931(2) MHz and B=-4.241(4) MHz. The isotope shift of the transition with
respect to 40Ca+ was measured to be 4134.713(5) MHz. We demonstrate the
existence of transitions that become independent of the first-order Zeeman
shift at non-zero low magnetic fields. These transitions might be better suited
for building a frequency standard than the well-known 'clock transitions'
between m=0 levels at zero magnetic field.Comment: corrected for sign errors in the hyperfine constants. No corrections
to were made to the data analysi
Locking Local Oscillator Phase to the Atomic Phase via Weak Measurement
We propose a new method to reduce the frequency noise of a Local Oscillator
(LO) to the level of white phase noise by maintaining (not destroying by
projective measurement) the coherence of the ensemble pseudo-spin of atoms over
many measurement cycles. This scheme uses weak measurement to monitor the phase
in Ramsey method and repeat the cycle without initialization of phase and we
call, "atomic phase lock (APL)" in this paper. APL will achieve white phase
noise as long as the noise accumulated during dead time and the decoherence are
smaller than the measurement noise. A numerical simulation confirms that with
APL, Allan deviation is averaged down at a maximum rate that is proportional to
the inverse of total measurement time, tau^-1. In contrast, the current atomic
clocks that use projection measurement suppress the noise only down to the
level of white frequency, in which case Allan deviation scales as tau^-1/2.
Faraday rotation is one of the possible ways to realize weak measurement for
APL. We evaluate the strength of Faraday rotation with 171Yb+ ions trapped in a
linear rf-trap and discuss the performance of APL. The main source of the
decoherence is a spontaneous emission induced by the probe beam for Faraday
rotation measurement. One can repeat the Faraday rotation measurement until the
decoherence become comparable to the SNR of measurement. We estimate this
number of cycles to be ~100 cycles for a realistic experimental parameter.Comment: 18 pages, 7 figures, submitted to New Journal of Physic
Evaporation of buffer gas-thermalized anions out of a multipole rf ion trap
We identify plain evaporation of ions as the fundamental loss mechanism out
of a multipole ion trap. Using thermalized negative Cl- ions we find that the
evaporative loss rate is proportional to a Boltzmann factor. This thermodynamic
description sheds new light on the dynamics of particles in time-varying
confining potentials. It specifically allows us to extract the effective depth
of the ion trap as the activation energy for evaporation. As a function of the
rf amplitude we find two distinct regimes related to the stability of motion of
the trapped ions. For low amplitudes the entire trap allows for stable motion
and the trap depth increases with the rf field. For larger rf amplitudes,
however, rapid energy transfer from the field to the ion motion can occur at
large trap radii, which leads to a reduction of the effective trapping volume.
In this regime the trap depth decreases again with increasing rf amplitude. We
give an analytical parameterization of the trap depth for various multipole
traps that allows predictions of the most favorable trapping conditions.Comment: Phys. Rev. Lett., in pres
Protecting subspaces by acting on the outside
Many quantum control tasks aim at manipulating the state of a quantum
mechanical system within a finite subspace of states. However, couplings to the
outside are often inevitable. Here we discuss strategies which keep the system
in the controlled subspace by applying strong interactions onto the outside.
This is done by drawing analogies to simple toy models and to the quantum Zeno
effect. Special attention is paid to the constructive use of dissipation in the
protection of subspaces.Comment: 16 pages, 10 figure
Ultrastable Optical Clock with Neutral Atoms in an Engineered Light Shift Trap
An ultrastable optical clock based on neutral atoms trapped in an optical
lattice is proposed. Complete control over the light shift is achieved by
employing the transition of
atoms as a "clock transition". Calculations of ac multipole polarizabilities
and dipole hyperpolarizabilities for the clock transition indicate that the
contribution of the higher-order light shifts can be reduced to less than 1
mHz, allowing for a projected accuracy of better than .Comment: 4 pages, 2 figures, accepted for publication in Phys. Rev. Let
Measure of phonon-number moments and motional quadratures through infinitesimal-time probing of trapped ions
A method for gaining information about the phonon-number moments and the
generalized nonlinear and linear quadratures in the motion of trapped ions (in
particular, position and momentum) is proposed, valid inside and outside the
Lamb-Dicke regime. It is based on the measurement of first time derivatives of
electronic populations, evaluated at the motion-probe interaction time t=0. In
contrast to other state-reconstruction proposals, based on measuring Rabi
oscillations or dispersive interactions, the present scheme can be performed
resonantly at infinitesimal short motion-probe interaction times, remaining
thus insensitive to decoherence processes.Comment: 10 pages. Accepted in JPhys
Sub-dekahertz ultraviolet spectroscopy of 199Hg+
Using a laser that is frequency-locked to a Fabry-Perot etalon of high
finesse and stability, we probe the 5d10 6s 2S_1/2 (F=0) - 5d9 6s 2D_5/2 (F=2)
Delta-m_F = 0 electric-quadrupole transition of a single laser-cooled 199Hg+
ion stored in a cryogenic radio-frequency ion trap. We observe
Fourier-transform limited linewidths as narrow as 6.7 Hz at 282 nm (1.06 X
10^15 Hz), yielding a line Q = 1.6 X 10^14. We perform a preliminary
measurement of the 5d9 6s2 2D_5/2 electric-quadrupole shift due to interaction
with the static fields of the trap, and discuss the implications for future
trapped-ion optical frequency standards.Comment: 4 pages, 4 figures, submitted for publicatio
Terahertz frequency standard based on three-photon coherent population trapping
A scheme for a THz frequency standard based on three-photon coherent
population trapping in stored ions is proposed. Assuming the propagation
directions of the three lasers obey the phase matching condition, we show that
stability of few 10 at one second can be reached with a precision
limited by power broadening to in the less favorable case. The
referenced THz signal can be propagated over long distances, the useful
information being carried by the relative frequency of the three optical
photons.Comment: article soumis a PRL le 21 mars 2007, accepte le 10 mai, version 2
(24/05/2007
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