756 research outputs found
Passive Cooling of a Micromechanical Oscillator with a Resonant Electric Circuit
We cool the fundamental mode of a miniature cantilever by capacitively
coupling it to a driven rf resonant circuit. Cooling results from the rf
capacitive force, which is phase shifted relative to the cantilever motion. We
demonstrate the technique by cooling a 7 kHz cantilever from room temperature
to 45 K, obtaining reasonable agreement with a model for the cooling, damping,
and frequency shift. Extending the method to higher frequencies in a cryogenic
system could enable ground state cooling and may prove simpler than related
optical experiments in a low temperature apparatus.Comment: 4 pages, 4 figures; minor changes to match published versio
Trapped-Ion Quantum Logic Utilizing Position-Dependent ac Stark Shifts
We present a scheme utilizing position-dependent ac Stark shifts for doing
quantum logic with trapped ions. By a proper choice of direction, position and
size, as well as power and frequency of a far-off-resonant Gaussian laser beam,
specific ac Stark shifts can be assigned to the individual ions, making them
distinguishable in frequency-space. In contrast to previous all-optical based
quantum gates with trapped ions, the present scheme enables individual
addressing of single ions and selective addressing of any pair of ions for
two-ion quantum gates, without using tightly focused laser beams. Furthermore,
the decoherence rate due to off-resonant excitations can be made negligible as
compared with other sources of decoherence.Comment: 5 pages, 4 figures. Submitted to Physical Review Letter
All-Optical Broadband Excitation of the Motional State of Trapped Ions
We have developed a novel all-optical broadband scheme for exciting,
amplifying and measuring the secular motion of ions in a radio frequency trap.
Oscillation induced by optical excitation has been coherently amplified to
precisely control and measure the ion's secular motion. Requiring only laser
line-of-sight, we have shown that the ion's oscillation amplitude can be
precisely controlled. Our excitation scheme can generate coherent motion which
is robust against variations in the secular frequency. Therefore, our scheme is
ideal to excite the desired level of oscillatory motion under conditions where
the secular frequency is evolving in time. Measuring the oscillation amplitude
through Doppler velocimetry, we have characterized the experimental parameters
and compared them with a molecular dynamics simulation which provides a
complete description of the system.Comment: 8 pages, 10 figure
Precision spectroscopy with two correlated atoms
We discuss techniques that allow for long coherence times in laser
spectroscopy experiments with two trapped ions. We show that for this purpose
not only entangled ions prepared in decoherence-free subspaces can be used but
also a pair of ions that are not entangled but subject to the same kind of
phase noise. We apply this technique to a measurement of the electric
quadrupole moment of the 3d D5/2 state of 40Ca+ and to a measurement of the
linewidth of an ultrastable laser exciting a pair of 40Ca+ ions
A trapped-ion local field probe
We introduce a measurement scheme that utilizes a single ion as a local field
probe. The ion is confined in a segmented Paul trap and shuttled around to
reach different probing sites. By the use of a single atom probe, it becomes
possible characterizing fields with spatial resolution of a few nm within an
extensive region of millimeters. We demonstrate the scheme by accurately
investigating the electric fields providing the confinement for the ion. For
this we present all theoretical and practical methods necessary to generate
these potentials. We find sub-percent agreement between measured and calculated
electric field values
Single-qubit-gate error below 10^-4 in a trapped ion
With a 9Be+ trapped-ion hyperfine-states qubit, we demonstrate an error
probability per randomized single-qubit gate of 2.0(2) x 10^-5, below the
threshold estimate of 10^-4 commonly considered sufficient for fault-tolerant
quantum computing. The 9Be+ ion is trapped above a microfabricated
surface-electrode ion trap and is manipulated with microwaves applied to a trap
electrode. The achievement of low single-qubit-gate errors is an essential step
toward the construction of a scalable quantum computer.Comment: 5 pages, 3 figures, 1 table; changed to match published versio
Direct measurement of the Wigner function by photon counting
We report a direct measurement of the Wigner function characterizing the
quantum state of a light mode. The experimental scheme is based on the
representation of the Wigner function as an expectation value of a displaced
photon number parity operator. This allowed us to scan the phase space
point-by-point, and obtain the complete Wigner function without using any
numerical reconstruction algorithms.Comment: 4 pages, REVTe
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