1,436 research outputs found
Quantum Darwinism requires an extra-theoretical assumption of encoding redundancy
Observers restricted to the observation of pointer states of apparatus cannot
conclusively demonstrate that the pointer of an apparatus A registers the state
of a system of interest S without perturbing S. Observers cannot, therefore,
conclusively demonstrate that the states of a system S are redundantly encoded
by pointer states of multiple independent apparatus without destroying the
redundancy of encoding. The redundancy of encoding required by quantum
Darwinism must, therefore, be assumed from outside the quantum-mechanical
formalism and without the possibility of experimental demonstration.Comment: 5 pages, 1 figure. Comments on foundational assumptions of W. Zurek
(2009) Nat Phys 5 181 (arXiv 0903.5082). v2 significant revision to improve
clarit
Symbiotic stars in the Local Group of Galaxies
Preliminary results of the ongoing search for symbiotic binary stars in the
Local Group of Galaxies are presented and discussed.Comment: Proceedings of Physics of Evolved Stars 2015: A Conference Dedicated
to the Memory of Olivier Chesneau, Nice, 8-12 June 201
Topological Schr\"odinger cats: Non-local quantum superpositions of topological defects
Topological defects (such as monopoles, vortex lines, or domain walls) mark
locations where disparate choices of a broken symmetry vacuum elsewhere in the
system lead to irreconcilable differences. They are energetically costly (the
energy density in their core reaches that of the prior symmetric vacuum) but
topologically stable (the whole manifold would have to be rearranged to get rid
of the defect). We show how, in a paradigmatic model of a quantum phase
transition, a topological defect can be put in a non-local superposition, so
that - in a region large compared to the size of its core - the order parameter
of the system is "undecided" by being in a quantum superposition of conflicting
choices of the broken symmetry. We demonstrate how to exhibit such a
"Schr\"odinger kink" by devising a version of a double-slit experiment suitable
for topological defects. Coherence detectable in such experiments will be
suppressed as a consequence of interaction with the environment. We analyze
environment-induced decoherence and discuss its role in symmetry breaking.Comment: 7 pages, 4 figure
Finite-Time Disentanglement via Spontaneous Emission
We show that under the influence of pure vacuum noise two entangled qubits
become completely disentangled in a finite time, and in a specific example we
find the time to be given by times the
usual spontaneous lifetime.Comment: revtex, 4 pages, 2 figure
PTOLEMY: A Proposal for Thermal Relic Detection of Massive Neutrinos and Directional Detection of MeV Dark Matter
We propose to achieve the proof-of-principle of the PTOLEMY project to directly detect the Cosmic Neutrino Background (CNB). Each of the technological challenges described in [1,2] will be targeted and hopefully solved by the use of the latest experimental developments and profiting from the low background environment provided by the LNGS underground site. The first phase will focus on the graphene technology for a tritium target and the demonstration of TES microcalorimetry with an energy resolution of better than 0.05 eV for low energy electrons. These technologies will be evaluated using the PTOLEMY prototype, proposed for underground installation, using precision HV controls to step down the kinematic energy of endpoint electrons to match the calorimeter dynamic range and rate capabilities. The second phase will produce a novel implementation of the EM filter that is scalable to the full target size and which demonstrates intrinsic triggering capability for selecting endpoint electrons. Concurrent with the CNB program, we plan to exploit and develop the unique properties of graphene to implement an intermediate program for direct directional detection of MeV dark matter [3,4]. This program will evaluate the radio-purity and scalability of the graphene fabrication process with the goal of using recently identified ultra-high radio-purity CO2 sources. The direct detection of the CNB is a snapshot of early universe dynamics recorded by the thermal relic neutrino yield taken at a time that predates the epochs of Big Bang Nucleosynthesis, the Cosmic Microwave Background and the recession of galaxies (Hubble Expansion). Big Bang neutrinos are believed to have a central role in the evolution of the Universe and a direct measurement with PTOLEMY will unequivocally establish the extent to which these predictions match present-day neutrino densities
A design for an electromagnetic filter for precision energy measurements at the tritium endpoint
We present a detailed description of the electromagnetic filter for the PTOLEMY project to directly detect the Cosmic Neutrino Background (CNB). Starting with an initial estimate for the orbital magnetic moment, the higher-order drift process of E X B is configured to balance the gradient-B drift motion of the electron in such a way as to guide the trajectory into the standing voltage potential along the mid-plane of the filter. As a function of drift distance along the length of the filter, the filter zooms in with exponentially increasing precision on the transverse velocity component of the electron kinetic energy. This yields a linear dimension for the total filter length that is exceptionally compact compared to previous techniques for electromagnetic filtering. The parallel velocity component of the electron kinetic energy oscillates in an electrostatic harmonic trap as the electron drifts along the length of the filter. An analysis of the phase-space volume conservation validates the expected behavior of the filter from the adiabatic invariance of the orbital magnetic moment and energy conservation following Liouville’s theorem for Hamiltonian systems
Solar mass-varying neutrino oscillations
We propose that the solar neutrino deficit may be due to oscillations of
mass-varying neutrinos (MaVaNs). This scenario elucidates solar neutrino data
beautifully while remaining comfortably compatible with atmospheric neutrino
and K2K data and with reactor antineutrino data at short and long baselines
(from CHOOZ and KamLAND). We find that the survival probability of solar MaVaNs
is independent of how the suppression of neutrino mass caused by the
acceleron-matter couplings varies with density. Measurements of MeV and lower
energy solar neutrinos will provide a rigorous test of the idea.Comment: 4 pages, 3 figures. Version to appear in PR
Neutrino physics with the PTOLEMY project: active neutrino properties and the light sterile case
The PTOLEMY project aims to develop a scalable design for a Cosmic Neutrino Background (CNB) detector, the first of its kind and the only one conceived that can look directly at the image of the Universe encoded in neutrino background produced in the first second after the Big Bang. The scope of the work for the next three years is to complete the conceptual design of this detector and to validate with direct measurements that the non-neutrino backgrounds are below the expected cosmological signal. In this paper we discuss in details the theoretical aspects of the experiment and its physics goals. In particular, we mainly address three issues. First we discuss the sensitivity of PTOLEMY to the standard neutrino mass scale. We then study the perspectives of the experiment to detect the CNB via neutrino capture on tritium as a function of the neutrino mass scale and the energy resolution of the apparatus. Finally, we consider an extra sterile neutrino with mass in the eV range, coupled to the active states via oscillations, which has been advocated in view of neutrino oscillation anomalies. This extra state would contribute to the tritium decay spectrum, and its properties, mass and mixing angle, could be studied by analyzing the features in the beta decay electron spectrum
Entropy and Wigner Functions
The properties of an alternative definition of quantum entropy, based on
Wigner functions, are discussed. Such definition emerges naturally from the
Wigner representation of quantum mechanics, and can easily quantify the amount
of entanglement of a quantum state. It is shown that smoothing of the Wigner
function induces an increase in entropy. This fact is used to derive some
simple rules to construct positive definite probability distributions which are
also admissible Wigner functionsComment: 18 page
Decoherence and the rate of entropy production in chaotic quantum systems
We show that for an open quantum system which is classically chaotic (a
quartic double well with harmonic driving coupled to a sea of harmonic
oscillators) the rate of entropy production has, as a function of time, two
relevant regimes: For short times it is proportional to the diffusion
coefficient (fixed by the system--environment coupling strength). For longer
times (but before equilibration) there is a regime where the entropy production
rate is fixed by the Lyapunov exponent. The nature of the transition time
between both regimes is investigated.Comment: Revtex, 4 pages, 3 figures include
- …