5,541 research outputs found
Observation of quantum jumps in a superconducting artificial atom
A continuously monitored quantum system prepared in an excited state will
decay to its ground state with an abrupt jump. The jump occurs stochastically
on a characteristic time scale T1, the lifetime of the excited state. These
quantum jumps, originally envisioned by Bohr, have been observed in trapped
atoms and ions, single molecules, photons, and single electrons in cyclotrons.
Here we report the first observation of quantum jumps in a macroscopic quantum
system, in our case a superconducting "artificial atom" or quantum bit (qubit)
coupled to a superconducting microwave cavity. We use a fast, ultralow-noise
parametric amplifier to amplify the microwave photons used to probe the qubit
state, enabling continuous high-fidelity monitoring of the qubit. This
technique represents a major step forward for solid state quantum information
processing, potentially enabling quantum error correction and feedback, which
are essential for building a quantum computer. Our technology can also be
readily integrated into hybrid circuits involving molecular magnets, nitrogen
vacancies in diamond, or semiconductor quantum dots.Comment: Updated draft including supplementary information. 8 pages, 6
figures. Supplementary videos are available on our website at
http://physics.berkeley.edu/research/siddiqi/docs/supps
Luminosity Function of the Perigalactocentric Region
We present H and K photometry of 42,000 stars in an area of 250 arcmin
centered on the Galactic center. We use the photometry to construct a
dereddened K band luminosity function (LF) for this region, excluding the
excessively crowded inner 2' of the Galaxy. This LF is intermediate between the
LF of Baade's window and the LF of inner 2' of the Galactic center. We
speculate that the bright stars in this region have an age which is
intermediate between the starburst population in the Galactic center and the
old bulge population. We present the coordinates and mags for 16 stars with
K_{0} < 5 for spectroscopic follow up.Comment: 25 pages. Tarred, gzipped and uuencoded. Includes LaTex source file,
Figures 3 to 9 and 5 Tables. Figures 1 and 2 are available at
ftp://bessel.mps.ohio-state.edu/pub/vijay . Submitted to Ap
Entwinement and the emergence of spacetime
It is conventional to study the entanglement between spatial regions of a
quantum field theory. However, in some systems entanglement can be dominated by
"internal", possibly gauged, degrees of freedom that are not spatially
organized, and that can give rise to gaps smaller than the inverse size of the
system. In a holographic context, such small gaps are associated to the
appearance of horizons and singularities in the dual spacetime. Here, we
propose a concept of entwinement, which is intended to capture this fine
structure of the wavefunction. Holographically, entwinement probes the
entanglement shadow -- the region of spacetime not probed by the minimal
surfaces that compute spatial entanglement in the dual field theory. We
consider the simplest example of this scenario -- a 2d conformal field theory
(CFT) that is dual to a conical defect in AdS3 space. Following our previous
work, we show that spatial entanglement in the CFT reproduces spacetime
geometry up to a finite distance from the conical defect. We then show that the
interior geometry up to the defect can be reconstructed from entwinement that
is sensitive to the discretely gauged, fractionated degrees of freedom of the
CFT. Entwinement in the CFT is related to non-minimal geodesics in the conical
defect geometry, suggesting a potential quantum information theoretic meaning
for these objects in a holographic context. These results may be relevant for
the reconstruction of black hole interiors from a dual field theory.Comment: v2: Sec. 4.3 amende
The entropy of a hole in spacetime
We compute the gravitational entropy of 'spherical Rindler space', a
time-dependent, spherically symmetric generalization of ordinary Rindler space,
defined with reference to a family of observers traveling along non-parallel,
accelerated trajectories. All these observers are causally disconnected from a
spherical region H (a 'hole') located at the origin of Minkowski space. The
entropy evaluates to S = A/4G, where A is the area of the spherical
acceleration horizon, which coincides with the boundary of H. We propose that S
is the entropy of entanglement between quantum gravitational degrees of freedom
supporting the interior and the exterior of the sphere H.Comment: 9 pages, 1 figure; v2: published version including updated reference
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