581 research outputs found
Ramsey interferometry with ultracold atoms
We examine the passage of ultracold two-level atoms through two separated
laser fields for the nonresonant case. We show that implications of the atomic
quantized motion change dramatically the behavior of the interference fringes
compared to the semiclassical description of this optical Ramsey
interferometer. Using two-channel recurrence relations we are able to express
the double-laser scattering amplitudes by means of the single-laser ones and to
give explicit analytical results. When considering slower and slower atoms, the
transmission probability of the system changes considerably from an
interference behavior to a regime where scattering resonances prevail. This may
be understood in terms of different families of trajectories that dominate the
overall transmission probability in the weak field or in the strong field
limit.Comment: 5 figures, 4 page
Symmetries and time operators
All covariant time operators with normalized probability distribution are
derived. Symmetry criteria are invoked to arrive at a unique expression for a
given Hamiltonian. As an application, a well known result for the arrival time
distribution of a free particle is generalized and extended. Interestingly, the
resulting arrival time distribution operator is connected to a particular,
positive, quantization of the classical current. For particles in a potential
we also introduce and study the notion of conditional arrival-time
distribution
Energy consumption for ion transport in a segmented Paul trap
There is recent interest in determining energy costs of shortcuts to
adiabaticity (STA), but different definitions of "cost" have been used. We
demonstrate the importance of taking into account the Control System (CS) for a
fair assessment of energy flows and consumptions. We model the energy
consumption and power to transport an ion by a STA protocol in a multisegmented
Paul trap. The ion is driven by an externally controlled, moving harmonic
oscillator. Even if no net ion- energy is gained at destination, setting the
time-dependent control parameters is a macroscopic operation that costs energy
and results in energy dissipation for the short time scales implied by the
intrinsically fast STA processes. The potential minimum is displaced by
modulating the voltages on control (dc) electrodes. A secondary effect of the
modulation, usually ignored as it does not affect the ion dynamics, is the
time- dependent energy shift of the potential minimum. The non trivial part of
the energy consumption is due to the electromotive forces to set the electrode
voltages through the low-pass filters required to preserve the electronic noise
from decohering the ion's motion. The results for the macroscopic CS (the Paul
trap) are compared to the microscopic power and energy of the ion alone.
Similarities are found -and may be used quantitatively to minimize costs- only
when the CS-dependent energy shift of the harmonic oscillator is included in
the ion energy
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