2,188 research outputs found
Catalysis always degrades external quantum correlations
Catalysts used in quantum resource theories need not be in isolation and
therefore are possibly correlated with external systems, which the agent does
not have access to. Do such correlations help or hinder catalysis, and does the
classicality or quantumness of such correlations matter? To answer this
question, we first focus on the existence of a non-invasively measurable
observable that yields the same outcomes for repeated measurements, since this
signifies macro-realism, a key property distinguishing classical systems from
quantum systems. We show that a system quantumly correlated with an external
system so that the joint state is necessarily perturbed by any repeatable
quantum measurement, also has the same property against general quantum
channels. Our full characterization of such systems called totally quantum
systems, solves the open problem of characterizing tomographically sensitive
systems raised in [Lie and Jeong, Phys. Rev. Lett. 130, 020802 (2023)]. An
immediate consequence is that a totally quantum system cannot catalyze any
quantum process, even when a measure of correlation with its environment is
arbitrarily low. It generalizes to a stronger result, that the mutual
information of totally quantum systems cannot be used as a catalyst either.
These results culminate in the conclusion that, out of the correlations that a
generic quantum catalyst has with its environment, only classical correlations
allow for catalysis, and therefore using a correlated catalyst is equivalent to
using an ensemble of uncorrelated catalysts.Comment: 5+7 pages, 1 figure, Comments are welcom
Uniqueness of quantum state over time function
A fundamental asymmetry exists within the conventional framework of quantum
theory between space and time, in terms of representing causal relations via
quantum channels and acausal relations via multipartite quantum states. Such a
distinction does not exist in classical probability theory. In effort to
introduce this symmetry to quantum theory, a new framework has recently been
proposed, such that dynamical description of a quantum system can be
encapsulated by a static quantum state over time. In particular, Fullwood and
Parzygnat recently proposed the state over time function based on the Jordan
product as a promising candidate for such a quantum state over time function,
by showing that it satisfies all the axioms required in the no-go result by
Horsman et al. However, it was unclear if the axioms induce a unique state over
time function. In this work, we demonstrate that the previously proposed axioms
cannot yield a unique state over time function. In response, we therefore
propose an alternative set of axioms that is operationally motivated, and
better suited to describe quantum states over any spacetime regions beyond two
points. By doing so, we establish the Fullwood-Parzygnat state over time
function as the essentially unique function satisfying all these operational
axioms.Comment: 5+4 pages, comments welcom
Charge states and magnetic ordering in LaMnO3/SrTiO3 superlattices
We investigated the magnetic and optical properties of
[(LaMnO3)n/(SrTiO3)8]20 (n = 1, 2, and 8) superlattices grown by pulsed laser
deposition. We found a weak ferromagnetic and semiconducting state developed in
all superlattices. An analysis of the optical conductivity showed that the
LaMnO3 layers in the superlattices were slightly doped. The amount of doping
was almost identical regardless of the LaMnO3 layer thickness up to eight unit
cells, suggesting that the effect is not limited to the interface. On the other
hand, the magnetic ordering became less stable as the LaMnO3 layer thickness
decreased, probably due to a dimensional effect.Comment: 17 pages including 4 figures, accepted for publication in Phys. Rev.
Effect of sintering temperature under high pressure in the uperconductivity for MgB2
We report the effect of the sintering temperature on the superconductivity of
MgB2 pellets prepared under a high pressure of 3 GPa. The superconducting
properties of the non-heated MgB2 in this high pressure were poor. However, as
the sintering temperature increased, the superconducting properties were vastly
enhanced, which was shown by the narrow transition width for the resistivity
and the low-field magnetizations. This shows that heat treatment under high
pressure is essential to improve superconducting properties. These changes were
found to be closely related to changes in the surface morphology observed using
scanning electron microscopy.Comment: 3 Pages including 3 figure
Use of a corrugated beam pipe as a passive deflector for bunch length measurements
We report the experimental demonstration of bunch length measurements using a corrugated metallic beam pipe as a passive deflector. The corrugated beam pipe has been adopted for reducing longitudinal chirping after the bunch compressors in several XFEL facilities worldwide. In the meantime, there have been attempts to measure the electron bunch's longitudinal current profile using the dipole wakefields generated in the corrugated pipe. Nevertheless, the bunch shape reconstructed from the nonlinearly deflected beam suffers from significant distortion, particularly near the head of the bunch. In this paper, we introduce an iterative process to improve the resolution of the bunch shape reconstruction. The ASTRA and ELEGANT simulations have been performed for pencil beam and cigar beam cases, in order to verify the effectiveness of the reconstruction process. To overcome the undesirable effects of transverse beam spreads, a measurement scheme involving both the corrugated beam pipe and the spectrometer magnet has been employed, both of which do not require a dedicated (and likely very expensive) rf system. A proof-of-principle experiment was carried out at Pohang Accelerator Laboratory (PAL) Injector Test Facility (ITF), and its results are discussed together with a comparison with the rf deflector measurement
Towards A Background Independent Quantum Gravity
We recapitulate the scheme of emergent gravity to highlight how a background
independent quantum gravity can be defined by quantizing spacetime itself.Comment: 25 pages, 2 figures, Proceedings of 7th International Conference
"Quantum Theory and Symmetries" (QTS-7) in Prague, Czech Republic, August,
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