16 research outputs found
Comment on ``Manipulating the frequency entangled states by an acoutic-optical modulator''
A recent theoretical paper [1] proposes a scheme for entanglement swapping
utilizing acousto-optic modulators without requiring a Bell-state measurement.
In this comment, we show that the proposal is flawed and no entanglement
swapping can occur without measurement.Comment: 6 pages, 2 figures submitted to Phys. Rev
Operational approach to open dynamics and quantifying initial correlations
A central aim of physics is to describe the dynamics of physical systems.
Schrodinger's equation does this for isolated quantum systems. Describing the
time evolution of a quantum system that interacts with its environment, in its
most general form, has proved to be difficult because the dynamics is dependent
on the state of the environment and the correlations with it. For discrete
processes, such as quantum gates or chemical reactions, quantum process
tomography provides the complete description of the dynamics, provided that the
initial states of the system and the environment are independent of each other.
However, many physical systems are correlated with the environment at the
beginning of the experiment. Here, we give a prescription of quantum process
tomography that yields the complete description of the dynamics of the system
even when the initial correlations are present. Surprisingly, our method also
gives quantitative expressions for the initial correlation.Comment: Completely re-written for clarity of presentation. 15 pages and 2
figure
Rapid sympathetic cooling to Fermi degeneracy on a chip
Neutral fermions present new opportunities for testing many-body condensed
matter systems, realizing precision atom interferometry, producing ultra-cold
molecules, and investigating fundamental forces. However, since their first
observation, quantum degenerate Fermi gases (DFGs) have continued to be
challenging to produce, and have been realized in only a handful of
laboratories. In this Letter, we report the production of a DFG using a simple
apparatus based on a microfabricated magnetic trap. Similar approaches applied
to Bose-Einstein Condensation (BEC) of 87Rb have accelerated evaporative
cooling and eliminated the need for multiple vacuum chambers. We demonstrate
sympathetic cooling for the first time in a microtrap, and cool 40K to Fermi
degeneracy in just six seconds -- faster than has been possible in conventional
magnetic traps. To understand our sympathetic cooling trajectory, we measure
the temperature dependence of the 40K-87Rb cross-section and observe its
Ramsauer-Townsend reduction.Comment: 5 pages, 4 figures (v3: new collision data, improved atom number
calibration, revised text, improved figures.