2,215 research outputs found
Displacement operators: the classical face of their quantum phase
In quantum mechanics, the operator representing the displacement of a system
in position or momentum is always accompanied by a path-dependent phase factor.
In particular, two non-parallel displacements in phase space do not compose
together in a simple way, and the order of these displacements leads to
different displacement composition phase factors. These phase factors are often
attributed to the nonzero commutator between quantum position and momentum
operators, but such a mathematical explanation might be unsatisfactory to
students who are after more physical insight. We present a couple of simple
demonstrations, using classical wave mechanics and classical particle
mechanics, that provide some physical intuition for the phase associated with
displacement operators.Comment: 14 pages, 4 figures, reorganized and reformatte
Spectroscopy of a synthetic trapped ion qubit
has been identified as an attractive ion for quantum
information processing due to the unique combination of its spin-1/2 nucleus
and visible wavelength electronic transitions. Using a microgram source of
radioactive material, we trap and laser-cool the synthetic = 133
radioisotope of barium II in a radio-frequency ion trap. Using the same, single
trapped atom, we measure the isotope shifts and hyperfine structure of the and
electronic transitions that are needed
for laser cooling, state preparation, and state detection of the clock-state
hyperfine and optical qubits. We also report the
electronic transition isotope shift for
the rare = 130 and 132 barium nuclides, completing the spectroscopic
characterization necessary for laser cooling all long-lived barium II isotopes
Time-Domain Measurement of Spontaneous Vibrational Decay of Magnetically Trapped NH
The v = 1 -> 0 radiative lifetime of NH (X triplet-Sigma-, v=1,N=0) is
determined to be tau_rad,exp. = 37.0 +/- 0.5 stat +2.0 / -0.8 sys miliseconds,
corresponding to a transition dipole moment of |mu_10| = 0.0540 + 0.0009 /
-0.0018 Debye. To achieve the long observation times necessary for direct
time-domain measurement, vibrationally excited NH (X triplet-Sigma-, v=1,N=0)
radicals are magnetically trapped using helium buffer-gas loading. Simultaneous
trapping and lifetime measurement of both the NH(v=1, N=0) and NH(v=0,N=0)
populations allows for accurate extraction of tau_rad,exp. Background helium
atoms are present during our measurement of tau_rad,exp., and the rate constant
for helium atom induced collisional quenching of NH(v=1,N=0) was determined to
be k_q < 3.9 * 10^-15 cm^3/s. This bound on k_q yields the quoted systematic
uncertainty on tau_rad,exp. Using an ab initio dipole moment function and an
RKR potential, we also determine a theoretical value of 36.99 ms for this
lifetime, in agreement with our experimental value. Our results provide an
independent determination of tau_rad,10, test molecular theory, and furthermore
demonstrate the efficacy of buffer-gas loading and trapping in determining
metastable radiative and collisional lifetimes.Comment: 10 pages + 3 figures (11 pages total) v2 has minor corrections and
explanations accepted for publication in PR
Polyqubit quantum processing
We describe the encoding of multiple qubits per atom in trapped atom quantum
processors and methods for performing both intra- and inter-atomic gates on
participant qubits without disturbing the spectator qubits stored in the same
atoms. We also introduce techniques for selective state preparation and
measurement of individual qubits that leave the information encoded in the
other qubits intact, a capability required for qubit quantum error correction.
The additional internal states needed for polyqubit processing are already
present in atomic processors, suggesting that the resource cost associated with
this multiplicative increase in qubit number could be a good bargain in the
short to medium term.Comment: 9 pages, 4 figure
Dipole-phonon quantum logic with trapped polar molecular ions
The interaction between the electric dipole moment of a trapped molecular ion
and the configuration of the confined Coulomb crystal couples the orientation
of the molecule to its motion. We consider the practical feasibility of
harnessing this interaction to initialize, process, and read out quantum
information encoded in molecular ion qubits without optically illuminating the
molecules. We present two schemes wherein a molecular ion can be entangled with
a co-trapped atomic ion qubit, providing, among other things, a means for
molecular state preparation and measurement. We also show that virtual phonon
exchange can significantly boost range of the intermolecular dipole-dipole
interaction, allowing strong coupling between widely-separated molecular ion
qubits
Magnetic trapping and Zeeman relaxation of imidogen (NH X-triplet-Sigma)
Imidogen (NH) radicals are magnetically trapped and their Zeeman relaxation
and energy transport collision cross sections with helium are measured.
Continuous buffer-gas loading of the trap is direct from a room-temperature
molecular beam. The Zeeman relaxation (inelastic) cross section of magnetically
trapped electronic, vibrational and rotational ground state imidogen in
collisions with He-3 is measured to be 3.8 +/- 1.1 E-19 cm^2 at 710 mK. The
NH-He energy transport cross section is also measured, indicating a ratio of
diffusive to inelastic cross sections of gamma = 7 E4 in agreement with the
recent theory of Krems et al. (PRA 68 051401(R) (2003))Comment: 12 pages, 3 figure
Phonon lasing from optical frequency comb illumination of a trapped ion
An atomic transition can be addressed by a single tooth of an optical
frequency comb if the excited state lifetime () is significantly longer
than the pulse repetition period (). In the crossover regime
between fully-resolved and unresolved comb teeth (), we observe Doppler cooling of a pre-cooled trapped atomic ion
by a single tooth of a frequency-doubled optical frequency comb. We find that
for initially hot ions, a multi-tooth effect gives rise to lasing of the ion's
harmonic motion in the trap, verified by acoustic injection locking. The gain
saturation of this phonon laser action leads to a comb of steady-state
oscillation amplitudes, allowing hot ions to be loaded directly into the trap
and laser cooled to crystallization despite the presence of hundreds of
blue-detuned teeth.Comment: 5 pages, 4 figure
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