162 research outputs found
Emergence of spatial spin-wave correlations in a cold atomic gas
Rydberg spin waves are optically excited in a quasi-one-dimensional atomic
sample of Rb atoms. Pair-wise spin-wave correlations are observed by a
spatially selective transfer of the quantum state onto a light field and
photoelectric correlation measurements of the light. The correlations are
interpreted in terms of the dephasing of multiply-excited spin waves by
long-range Rydberg interactions
Entanglement of light-shift compensated atomic spin waves with telecom light
Entanglement of a 795 nm light polarization qubit and an atomic Rb spin wave
qubit for a storage time of 0.1 s is observed by measuring the violation of
Bell's inequality (S = 2.65 \pm 0.12). Long qubit storage times are achieved by
pinning the spin wave in a 1064 nm wavelength optical lattice, with a
magic-valued magnetic field superposed to eliminate lattice-induced dephasing.
Four-wave mixing in a cold Rb gas is employed to perform light qubit conversion
between near infra red (795 nm) and telecom (1367 nm) wavelengths, and after
propagation in a telecom fiber, to invert the conversion process. Observed Bell
inequality violation (S = 2.66 \pm 0.09), at 10 ms storage, confirms
preservation of memory/light entanglement through the two stages of light qubit
frequency conversion.Comment: 5 pages, 3 figure
Vertically integrated holdings in the system of developing the national complex of iron and steel industry of Russia
This article shows brief results of analyzing the competitiveness of Russian vertically integrated holdings and independent enterprises of the iron and steel industry. Besides, it indicates key areas of this industry development in the external and internal market aspect. The promotion of Russian iron and steel products on the external market can be successful only if the production of enterprises is refocused from creating products of low technological conversions to creating products of high technological conversions
Electrochemistry at nanoscale electrodes : individual single-walled carbon nanotubes (SWNTs) and SWNT-templated metal nanowires
Individual nanowires (NWs) and native single-walled carbon nanotubes (SWNTs) can be readily used as well-defined nanoscale electrodes (NSEs) for voltammetric analysis. Here, the simple photolithography-free fabrication of submillimeter long Au, Pt, and Pd NWs, with sub-100 nm heights, by templated electrodeposition onto ultralong flow-aligned SWNTs is demonstrated. Both individual Au NWs and SWNTs are employed as NSEs for electron-transfer (ET) kinetic quantification, using cyclic voltammetry (CV), in conjunction with a microcapillary-based electrochemical method. A small capillary with internal diameter in the range 30â70 ÎŒm, filled with solution containing a redox-active mediator (FcTMA+ ((trimethylammonium)methylferrocene), Fe(CN)64â, or hydrazine) is positioned above the NSE, so that the solution meniscus completes an electrochemical cell. A 3D finite-element model, faithfully reproducing the experimental geometry, is used to both analyze the experimental CVs and derive the rate of heterogeneous ET, using ButlerâVolmer kinetics. For a 70 nm height Au NW, intrinsic rate constants, k0, up to ca. 1 cm sâ1 can be resolved. Using the same experimental configuration the electrochemistry of individual SWNTs can also be accessed. For FcTMA+/2+ electrolysis the simulated ET kinetic parameters yield very fast ET kinetics (k0 > 2 ± 1 cm sâ1). Some deviation between the experimental voltammetry and the idealized model is noted, suggesting that double-layer effects may influence ET at the nanoscale
Observation of coherent many-body Rabi oscillations
A two-level quantum system coherently driven by a resonant electromagnetic
field oscillates sinusoidally between the two levels at frequency
which is proportional to the field amplitude [1]. This phenomenon, known as the
Rabi oscillation, has been at the heart of atomic, molecular and optical
physics since the seminal work of its namesake and coauthors [2]. Notably, Rabi
oscillations in isolated single atoms or dilute gases form the basis for
metrological applications such as atomic clocks and precision measurements of
physical constants [3]. Both inhomogeneous distribution of coupling strength to
the field and interactions between individual atoms reduce the visibility of
the oscillation and may even suppress it completely. A remarkable
transformation takes place in the limit where only a single excitation can be
present in the sample due to either initial conditions or atomic interactions:
there arises a collective, many-body Rabi oscillation at a frequency
involving all N >> 1 atoms in the sample [4]. This is true even
for inhomogeneous atom-field coupling distributions, where single-atom Rabi
oscillations may be invisible. When one of the two levels is a strongly
interacting Rydberg level, many-body Rabi oscillations emerge as a consequence
of the Rydberg excitation blockade. Lukin and coauthors outlined an approach to
quantum information processing based on this effect [5]. Here we report initial
observations of coherent many-body Rabi oscillations between the ground level
and a Rydberg level using several hundred cold rubidium atoms. The strongly
pronounced oscillations indicate a nearly complete excitation blockade of the
entire mesoscopic ensemble by a single excited atom. The results pave the way
towards quantum computation and simulation using ensembles of atoms
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