17,496 research outputs found
Test of quantum chemistry in vibrationally-hot hydrogen molecules
Precision measurements are performed on highly excited vibrational quantum
states of molecular hydrogen. The rovibrational levels of H
(), lying only cm below the first dissociation
limit, were populated by photodissociation of HS and their level energies
were accurately determined by two-photon Doppler-free spectroscopy. A
comparison between the experimental results on level energies with the
best \textit{ab initio} calculations shows good agreement, where the present
experimental accuracy of cm is more precise than
theory, hence providing a gateway to further test theoretical advances in this
benchmark quantum system.Comment: 5 pages, 4 figures, and 2 table
Qudit-Basis Universal Quantum Computation using Interactions
We prove that universal quantum computation can be realized---using only
linear optics and (three-wave mixing) interactions---in any
-dimensional qudit basis of the -pump-photon subspace. First, we
exhibit a strictly universal gate set for the qubit basis in the
one-pump-photon subspace. Next, we demonstrate qutrit-basis universality by
proving that Hamiltonians and photon-number operators generate the
full Lie algebra in the two-pump-photon subspace, and showing
how the qutrit controlled- gate can be implemented with only linear optics
and interactions. We then use proof by induction to obtain our
general qudit result. Our induction proof relies on coherent photon
injection/subtraction, a technique enabled by interaction between
the encoding modes and ancillary modes. Finally, we show that coherent photon
injection is more than a conceptual tool in that it offers a route to preparing
high-photon-number Fock states from single-photon Fock states.Comment: 9 pages, 3 figure
High-precision laser spectroscopy of the CO A - X (2,0), (3,0) and (4,0) bands
High-precision two-photon Doppler-free frequency measurements have been
performed on the CO A - X fourth-positive system (2,0),
(3,0), and (4,0) bands. Absolute frequencies of forty-three transitions, for
rotational quantum numbers up to , have been determined at an accuracy
of cm, using advanced techniques of two-color 2+1'
resonance-enhanced multi-photon ionization, Sagnac interferometry,
frequency-chirp analysis on the laser pulses, and correction for AC-Stark
shifts. The accurate transition frequencies of the CO A - X
system are of relevance for comparison with astronomical data in the search for
possible drifts of fundamental constants in the early universe. The present
accuracies in laboratory wavelengths of may be considered exact for the purpose of such comparisons.Comment: 13 pages, 6 figures, The Journal of Chemical Physics (2015) accepte
High-speed measurement of rotational anisotropy nonlinear optical harmonic generation using position sensitive detection
We present a method of performing high-speed rotational anisotropy nonlinear
optical harmonic generation experiments at rotational frequencies of several
hertz by projecting the harmonic light reflected at different angles from a
sample onto a stationary position sensitive detector. The high rotational speed
of the technique, to times larger than existing methods, permits
precise measurements of the crystallographic and electronic symmetries of
samples by averaging over low frequency laser power, beam pointing, and pulse
width fluctuations. We demonstrate the sensitivity of our technique by
resolving the bulk four-fold rotational symmetry of GaAs about its [001] axis
using second harmonic generation
Berry phases in superconducting transitions
I generalize the concept of Berry's geometrical phase for quasicyclic
Hamiltonians to the case in which the ground state evolves adiabatically to an
excited state after one cycle, but returns to the ground state after an integer
number of cycles. This allows to extend the charge Berry phase gamma_c related
to the macroscopic polarization, to many-body systems with fractional number of
particles per site. Under certain conditions, gamma_c and the spin Berry phase
gamma_s jump in pi at the boundary of superconducting phases. In the extended
Hubbard chain with on-site attraction U and nearest-neighbor interaction V at
quarter filling, the transitions detected agree very well with exact results in
two limits solved by the Bethe ansatz, and with previous numerical studies. In
chains with spin SU(2) symmetry, gamma_s jumps when a spin gap opens.Comment: 5 pages, 3 figures, accepted in Europhys. Let
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