821 research outputs found
Bound on the closed quantum dynamics under stochastic noise
Quantum information technologies require careful control for preparing a
desired target state used for an information resource. The one of the obstacles
is the stochastic noise on the control Hamiltonian, under which the realistic
control performance is severely limited. Therefore, the reachability analysis,
which in our scenario quantifying the distance between the obtained state under
the noise and the target state, is of great importance. This paper gives a
lower bound of the fidelity for a closed quantum system under the stochastic
noise. Note that this bound is computable without considering the stochastic
process and needing the full time-dependent dynamics of the states. We
demonstrate the actual tightness of this bound via numerical simulation.Comment: 5 pages, 2 figure
Bound on the distance between controlled quantum state and target state under decoherence
To implement quantum information technologies, carefully designed control for
preparing a desired state plays a key role. However, in realistic situation,
the actual performance of those methodologies is severely limited by
decoherence. Therefore, it is important to evaluate how close we can steer the
controlled state to a desired target state under decoherence. In this paper, we
provide an upper bound of the distance between the two controlled quantum
systems in the presence and absence of decoherence. The bound quantifies the
degree of achievement of the control for a given target state under
decoherence, and can be straightforwardly calculated without solving any
equation. Moreover, the upper bound is applied to derive a theoretical limit of
the probability for obtaining the target state under decoherence.Comment: 11 pages, 2 figur
An ytterbium quantum gas microscope with narrow-line laser cooling
We demonstrate site-resolved imaging of individual bosonic
atoms in a Hubbard-regime two-dimensional optical lattice
with a short lattice constant of 266 nm. To suppress the heating by probe light
with the - transition of the wavelength = 399 nm for
high-resolution imaging and preserve atoms at the same lattice sites during the
fluorescence imaging, we simultaneously cool atoms by additionally applying
narrow-line optical molasses with the - transition of the
wavelength = 556 nm. We achieve a low temperature of $T = 7.4(1.3)\
\mu\mathrm{K}$, corresponding to a mean oscillation quantum number along the
horizontal axes of 0.22(4) during imaging process. We detect on average 200
fluorescence photons from a single atom within 400 ms exposure time, and
estimate the detection fidelity of 87(2)%. The realization of a quantum gas
microscope with enough fidelity for Yb atoms in a Hubbard-regime optical
lattice opens up the possibilities for studying various kinds of quantum
many-body systems such as Bose and Fermi gases, and their mixtures, and also
long-range-interacting systems such as Rydberg states.Comment: 14 pages, 6 figure
Cosmic R-string, R-tube and Vacuum Instability
We show that a cosmic string associated with spontaneous symmetry
breaking gives a constraint for supersymmetric model building. In some models,
the string can be viewed as a tube-like domain wall with a winding number
interpolating a false vacuum and a true vacuum. Such string causes
inhomogeneous decay of the false vacuum to the true vacuum via rapid expansion
of the radius of the tube and hence its formation would be inconsistent with
the present Universe. However, we demonstrate that there exist metastable
solutions which do not expand rapidly. Furthermore, when the true vacua are
degenerate, the structure inside the tube becomes involved. As an example, we
show a "bamboo"-like solution, which suggests a possibility observing an
information of true vacua from outside of the tube through the shape and the
tension of the tube.Comment: 28 pages, 17 figures, v2: references added, improved arguments in sec
3.5.
Origin of the anomalous mass renormalization in metallic quantum well states of correlated oxide SrVO
angle-resolved photoemission spectroscopy (ARPES) has been
performed on SrVO ultrathin films, which show metallic quantum well (QW)
states, to unveil the origin of the anomalous mass enhancement in the QW
subbands. The line-shape analysis of the ARPES spectra reveals that the
strength of the electron correlation increases as the subband bottom energy
approaches the Fermi level. These results indicate that the anomalous
subband-dependent mass enhancement mainly arises from the quasi-one-dimensional
character of confined V states as a result of their orbital-selective
quantization.Comment: 6 pages, 3 figure
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