127 research outputs found
Applicability of Rydberg atoms to quantum computers
Applicability of Rydberg atoms to quantum computers is examined from
experimental point of view. In many theoretical proposals appeared recently,
excitation of atoms into highly excited Rydberg states was considered as a way
to achieve quantum entanglement in cold atomic ensembles via dipole-dipole
interaction that could be strong for Rydberg atoms. Appropriate conditions to
realize a conditional quantum phase gate have been analyzed. We also present
the results of modeling experiments on microwave spectroscopy of single- and
multi-atom excitations at the one-photon 37S-37P and two-photon 37S-38S
transitions in an ensemble of a few sodium Rydberg atoms. The microwave spectra
were investigated for various final states of the ensemble initially prepared
in its ground state. The quantum NOT operation with single atoms was found to
be affected by the Doppler effect and fluctuations of the microwave field. The
spectrum of full excitation of several Rydberg atoms was much narrower than
that of a single atom. This effect might be useful for the high-resolution
spectroscopy. The results may be also applied to the studies on collective
laser excitation of ground-state atoms aiming to realize quantum gates.Comment: 12 pages, 8 EPS figures, Revtex4. Old references corrected, new adde
Effect of finite detection efficiency on the observation of the dipole-dipole interaction of a few Rydberg atoms
We have developed a simple analytical model describing multi-atom signals
that are measured in experiments on dipole-dipole interaction at resonant
collisions of a few Rydberg atoms. It has been shown that finite efficiency of
the selective field-ionization detector leads to the mixing up of the spectra
of resonant collisions registered for various numbers of Rydberg atoms. The
formulas which help to estimate an appropriate mean Rydberg atom number for a
given detection efficiency are presented. We have found that a measurement of
the relation between the amplitudes of collisional resonances observed in the
one- and two-atom signals provides a straightforward determination of the
absolute detection efficiency and mean Rydberg atom number. We also performed a
testing experiment on resonant collisions in a small excitation volume of a
sodium atomic beam. The resonances observed for 1 to 4 detected Rydberg atoms
have been analyzed and compared with theory.Comment: 10 pages, 4 figures; equations 8,9,18,19,23,26-31, figures 3 and
4(d), and measurements revised in version
Quasiclassical calculations of BBR-induced depopulation rates and effective lifetimes of Rydberg nS, nP and nD alkali-metal atoms with n < 80
Rates of depopulation by blackbody radiation (BBR) and effective lifetimes of
alkali-metal \textit{nS}, \textit{n}P and \textit{nD} Rydberg states have been
calculated in a wide range of principal quantum numbers at the
ambient temperatures of 77, 300 and 600 K. Quasiclassical formulas were used to
calculate the radial matrix elements of the dipole transitions from Rydberg
states. Good agreement of our numerical results with the available theoretical
and experimental data has been found. We have also obtained simple analytical
formulas for estimates of effective lifetimes and BBR-induced depopulation
rates, which well agree with the numerical data.Comment: 12 pages, 6 figures, 8 tables. Typo in Eq.16 corrected in V2. Typos
in Eq.5 and Eq.9 corrected in V3. Error in calculation of Rb nP_{3/2}
effective lifetimes corrected in V4: see new data in Table II and Table VII,
Erratum to be published in PR
Ionization of Rydberg atoms by blackbody radiation
We have studied an ionization of alkali-metal Rydberg atoms by blackbody
radiation (BBR). The results of the theoretical calculations of ionization
rates of Li, Na, K, Rb and Cs Rydberg atoms are presented. Calculations have
been performed for nS, nP and nD states which are commonly used in a variety of
experiments, at principal quantum numbers n=8-65 and at the three ambient
temperatures of 77, 300 and 600 K. A peculiarity of our calculations is that we
take into account the contributions of BBR-induced redistribution of population
between Rydberg states prior to photoionization and field ionization by
extraction electric field pulses. The obtained results show that these
phenomena affect both the magnitude of measured ionization rates and shapes of
their dependences on n. A Cooper minimum for BBR-induced transitions between
bound Rydberg states of Li has been found. The calculated ionization rates are
compared with our earlier measurements of BBR-induced ionization rates of Na nS
and nD Rydberg states with n=8-20 at 300 K. A good agreement for all states
except nS with n>15 is observed. Useful analytical formulas for quick
estimation of BBR ionization rates of Rydberg atoms are presented. Application
of BBR-induced ionization signal to measurements of collisional ionization
rates is demonstrated.Comment: 36 pages, 16 figures. Paper is revised following NJP referees'
comments and suggestion
Effect of photoions on the line shapes of the F\"orster resonance and microwave transitions in cold rubidium Rydberg atoms
Experiments on the spectroscopy of the F\"orster resonance Rb(37P)+Rb(37P) ->
Rb(37S)+Rb(38S) and microwave transitions nP -> n'S, n'D between Rydberg states
of cold Rb atoms in a magneto-optical trap have been performed. Under ordinary
conditions, all spectra exhibited a 2-3 MHz line width independently of the
interaction time of atoms with each other or with microwave radiation, although
the ultimate resonance width should be defined by the inverse interaction time.
Analysis of the experimental conditions has shown that the main source of the
line broadening was the inhomogeneous electric field of cold photoions appeared
at the excitation of initial Rydberg nP states by broadband pulsed laser
radiation. Using an additional pulse of the electric field, which rapidly
removed the photoions after the laser pulse, lead to a substantial narrowing of
the microwave and F\"orster resonances. An analysis of various sources of the
line broadening in cold Rydberg atoms has been conducted.Comment: 10 pages, 6 figure
Deterministic single-atom excitation via adiabatic passage and Rydberg blockade
We propose to use adiabatic rapid passage with a chirped laser pulse in the
strong dipole blockade regime to deterministically excite only one Rydberg atom
from randomly loaded optical dipole traps or optical lattices. The chirped
laser excitation is shown to be insensitive to the random number \textit{N} of
the atoms in the traps. Our method overcomes the problem of the
dependence of the collective Rabi frequency, which was the main obstacle for
deterministic single-atom excitation in the ensembles with unknown \textit{N},
and can be applied for single-atom loading of dipole traps and optical
lattices.Comment: 6 pages, 5 figures. Version 5 is expanded and submitted to PRA. Typo
in Fig.4 corrected in Version 2. Version 3 and 4 are duplicates of V
- …