34 research outputs found
Lessons on Eternal Traversable Wormholes in AdS
We attempt to construct eternal traversable wormholes connecting two
asymptotically AdS regions by introducing a static coupling between their dual
CFTs. We prove that there are no semiclassical traversable wormholes with
Poincar\'e invariance in the boundary directions in higher than two spacetime
dimensions. We critically examine the possibility of evading our result by
coupling a large number of bulk fields. Static, traversable wormholes with less
symmetry may be possible, and could be constructed using the ingredients we
develop here.Comment: 22 pages, 4 figures. v2: minor additions, matches published versio
Action, entropy and pair creation rate of charged black holes in de Sitter space
We compute and clarify the interpretation of the on-shell Euclidean action
for Reissner-Nordstr\"{o}m black holes in de Sitter space. We show the on-shell
action is minus the sum of the black hole and cosmological horizon entropy for
arbitrary mass and charge in any number of dimensions. This unifying expression
helps to clear up a confusion about the Euclidean actions of extremal and
ultracold black holes in de Sitter, as they can be understood as special cases
of the general expression. We then use this result to estimate the probability
for the pair creation of black holes with arbitrary mass and charge in an empty
de Sitter background, by employing the formalism of constrained instantons.
Finally, we comment that the decay of charged de Sitter black holes is expected
to be governed by the gradient flow of the entropy function, and that as a
consequence, as long as the regime of light, superradiant, rapid charge
emission is excluded, the effective decay may be described by the tunneling
formalism.Comment: 27 pages, 9 figure
On the Euclidean Action of de Sitter Black Holes and Constrained Instantons
We compute the on-shell Euclidean action of Schwarzschild-de Sitter black
holes, and take their contributions in the gravitational path integral into
account using the formalism of constrained instantons. Although Euclidean de
Sitter black hole geometries have conical singularities for generic masses,
their on-shell action is finite and is shown to be independent of the Euclidean
time periodicity and equal to minus the sum of the black hole and cosmological
horizon entropy. We apply this result to compute the probability for a
nonrotating, neutral arbitrary mass black hole to nucleate spontaneously in
empty de Sitter space, which separates into a constant and a "non-perturbative"
contribution, the latter corresponding to the proper saddle-point instanton in
the Nariai limit. We also speculate on some further applications of our
results, most notably as potential non-perturbative corrections to correlators
in the de Sitter vacuum.Comment: 34 pages, 15 figures, added further references and clarifications.
Revised version for SciPos
Suppressing quantum errors by scaling a surface code logical qubit
Practical quantum computing will require error rates that are well below what
is achievable with physical qubits. Quantum error correction offers a path to
algorithmically-relevant error rates by encoding logical qubits within many
physical qubits, where increasing the number of physical qubits enhances
protection against physical errors. However, introducing more qubits also
increases the number of error sources, so the density of errors must be
sufficiently low in order for logical performance to improve with increasing
code size. Here, we report the measurement of logical qubit performance scaling
across multiple code sizes, and demonstrate that our system of superconducting
qubits has sufficient performance to overcome the additional errors from
increasing qubit number. We find our distance-5 surface code logical qubit
modestly outperforms an ensemble of distance-3 logical qubits on average, both
in terms of logical error probability over 25 cycles and logical error per
cycle ( compared to ). To investigate
damaging, low-probability error sources, we run a distance-25 repetition code
and observe a logical error per round floor set by a single
high-energy event ( when excluding this event). We are able
to accurately model our experiment, and from this model we can extract error
budgets that highlight the biggest challenges for future systems. These results
mark the first experimental demonstration where quantum error correction begins
to improve performance with increasing qubit number, illuminating the path to
reaching the logical error rates required for computation.Comment: Main text: 6 pages, 4 figures. v2: Update author list, references,
Fig. S12, Table I
Measurement-induced entanglement and teleportation on a noisy quantum processor
Measurement has a special role in quantum theory: by collapsing the
wavefunction it can enable phenomena such as teleportation and thereby alter
the "arrow of time" that constrains unitary evolution. When integrated in
many-body dynamics, measurements can lead to emergent patterns of quantum
information in space-time that go beyond established paradigms for
characterizing phases, either in or out of equilibrium. On present-day NISQ
processors, the experimental realization of this physics is challenging due to
noise, hardware limitations, and the stochastic nature of quantum measurement.
Here we address each of these experimental challenges and investigate
measurement-induced quantum information phases on up to 70 superconducting
qubits. By leveraging the interchangeability of space and time, we use a
duality mapping, to avoid mid-circuit measurement and access different
manifestations of the underlying phases -- from entanglement scaling to
measurement-induced teleportation -- in a unified way. We obtain finite-size
signatures of a phase transition with a decoding protocol that correlates the
experimental measurement record with classical simulation data. The phases
display sharply different sensitivity to noise, which we exploit to turn an
inherent hardware limitation into a useful diagnostic. Our work demonstrates an
approach to realize measurement-induced physics at scales that are at the
limits of current NISQ processors
Non-Abelian braiding of graph vertices in a superconducting processor
Indistinguishability of particles is a fundamental principle of quantum
mechanics. For all elementary and quasiparticles observed to date - including
fermions, bosons, and Abelian anyons - this principle guarantees that the
braiding of identical particles leaves the system unchanged. However, in two
spatial dimensions, an intriguing possibility exists: braiding of non-Abelian
anyons causes rotations in a space of topologically degenerate wavefunctions.
Hence, it can change the observables of the system without violating the
principle of indistinguishability. Despite the well developed mathematical
description of non-Abelian anyons and numerous theoretical proposals, the
experimental observation of their exchange statistics has remained elusive for
decades. Controllable many-body quantum states generated on quantum processors
offer another path for exploring these fundamental phenomena. While efforts on
conventional solid-state platforms typically involve Hamiltonian dynamics of
quasi-particles, superconducting quantum processors allow for directly
manipulating the many-body wavefunction via unitary gates. Building on
predictions that stabilizer codes can host projective non-Abelian Ising anyons,
we implement a generalized stabilizer code and unitary protocol to create and
braid them. This allows us to experimentally verify the fusion rules of the
anyons and braid them to realize their statistics. We then study the prospect
of employing the anyons for quantum computation and utilize braiding to create
an entangled state of anyons encoding three logical qubits. Our work provides
new insights about non-Abelian braiding and - through the future inclusion of
error correction to achieve topological protection - could open a path toward
fault-tolerant quantum computing
Personality dimensions emerging during adolescence and young adulthood are underpinned by a single latent trait indexing impairment in social functioning
Shocks and Information Exchange in de Sitter Space
We discuss some implications of recent progress in understanding the black
hole information paradox for complementarity in de Sitter space. Extending
recent work by two of the authors, we describe a bulk procedure that allows
information expelled through the cosmological horizon to be received by an
antipodal observer. Generically, this information transfer takes a scrambling
time . We emphasize that this procedure relies
crucially on selection of the Bunch-Davies vacuum state, interpreted as the
thermofield double state that maximally entangles two antipodal static patches.
The procedure also requires the presence of an (entangled) energy reservoir,
created by the collection of Hawking modes from the cosmological horizon. We
show how this procedure avoids a cloning paradox and comment on its
implications.Comment: 21 pages + appendix. v2: added references, minor clarifications. v3:
matches published versio
Dynamics of mud banks and sandy urban beaches in French Guiana, South America
Beach rotation is a widely described process characterized by periodic alternations in sediment transport involving erosion at one end of the beach and accretion at the other. The 1500-km-long coast of the Guianas, South America, is a unique system dominated by large migrating mud banks, muddy, mangrove-rich shorelines, and rare sandy beaches. Interactions between waves and the rare beaches on this coast are affected by the mud banks which are separated by âinter-bankâ areas. Kourou beach is situated near the site of the European Space Agencyâs satellite-launching pad in French Guiana. The beach has maintained multi-decadal stability, but its interaction with mud banks has led to phases of severe erosion. To understand these changes, which constitute a risk for the urban front of Kourou, we combined a mesoscale temporal (1950â2017) analysis of shoreline fluctuations with a short-term approach based on photogrammetric monitoring of beach change conducted in 2017â2018 and on bathymetric surveys of the nearshore zone. The results show that Kourou beach evolves in a context of ârotationâ, a process involving periodic alternations in beach erosion and recovery. Rotation is characterized during inter-bank phases by ânormalâ sand transport to the northwest generated by the prevailing NE waves, and during mud-bank phases by drift reversal to the southeast generated by refraction of these waves at the leading front of a bank. Due to the aperiodic nature of these bank and inter-bank phases, erosion and accretion involved in beach rotation may prevail over variable periods of time (several years to decades). The large mud banks migrating from east to west first protect the southeastern sector of the beach, blocking the ânormalâ northwestward longshore sand transport, but generating, through differential refraction, southeastward counter-drift. These processes and the irregular timescale of beach rotation they entail have not been compatible with the recent urbanization of the beach front in the southeastern sector, resulting in erosion and a sense of threat to beachfront property. Insight gained from an understanding of the rotation process and its irregular timescales should contribute to better beach-front management
Assessing SfM-Photogrammetry potential at micro-scale on a rapidly evolving mud-bank: case study on a mesocosm study within pioneer mangroves in French Guiana (South America)
International audienceMud banks are the loci of rich bio-geo-chemical processes occuring rapidly at infra-tide frequency. Their surface topography is commonly affected by many of these processes, including bioturbation, water drainage or dessica-tion. Quantifying surface morphology and changes on a mud bank at the micro-scale is a challenging task due to a number of issues. First, the water-saturated nature of the soil makes it difficult to measure High Resolution Topography (HRT) with classical methods. Second, setting up an instrumented experiment without disrupting the signal being studied is hardly achieved at micro-scale. Finally, the highly mobile nature of this environment enhancing strong spatio-temporal heterogeneity is hard to capture. Terrestrial Laser Scanning (TLS) and SfM (Surface from Motion)-Photogrammetry are two techniques that enable mapping of micro-scale features, but the first technique is not suitable because of the poor quality of the backscat-tered laser signal on wet surfaces and the need to set up several measuring stations on a complex, unstable substrate. Thus, we set up an experiment to assess the feasibility and the accuracy of SfM in such a context. We took the opportunity of the installation of a pontoon dedicated to the study of bio-geochemical processes within benthic mesocosms installed on a mud bank inhabited by pioneer mangroves trees to develop an adapted photogrammetry protocol based on a full-frame remotely triggered camera sensor mounted on a pole. The incident light on the surface was also controlled with a light-diffusing device. We obtained sub-millimetric resolution 3D-topography and visible imagery. Surveys were carried out every 2 hours at low tide to detect surface changes due to water content variation as well as bioturbation mainly caused by crabs digging galleries and feeding on sediment surface. Both the qualitative and quantitative results seem very promising and lead us to expect new insights into heterogeneous surface processes on a highly dynamic mud bank. Remaining issues are finding appropriate validation data at such a high level of resolution in order to assess accuracy, and developing an acquisition method at a frequency high enough to enable us to decipher bulk soil movement from local changing features