2,307 research outputs found
Macroscopic entanglement of many-magnon states
We study macroscopic entanglement of various pure states of a one-dimensional
N-spin system with N>>1. Here, a quantum state is said to be macroscopically
entangled if it is a superposition of macroscopically distinct states. To judge
whether such superposition is hidden in a general state, we use an essentially
unique index p: A pure state is macroscopically entangled if p=2, whereas it
may be entangled but not macroscopically if p<2. This index is directly related
to the stability of the state. We calculate the index p for various states in
which magnons are excited with various densities and wavenumbers. We find
macroscopically entangled states (p=2) as well as states with p=1. The former
states are unstable in the sense that they are unstable against some local
measurements. On the other hand, the latter states are stable in the senses
that they are stable against local measurements and that their decoherence
rates never exceed O(N) in any weak classical noises. For comparison, we also
calculate the von Neumann entropy S(N) of a subsystem composed of N/2 spins as
a measure of bipartite entanglement. We find that S(N) of some states with p=1
is of the same order of magnitude as the maximum value N/2. On the other hand,
S(N) of the macroscopically entangled states with p=2 is as small as O(log N)<<
N/2. Therefore, larger S(N) does not mean more instability. We also point out
that these results are analogous to those for interacting many bosons.
Furthermore, the origin of the huge entanglement, as measured either by p or
S(N), is discussed to be due to the spatial propagation of magnons.Comment: 30 pages, 5 figures. The manuscript has been shortened and typos have
been fixed. Data points of figures have been made larger in order to make
them clearly visibl
Many body localization and thermalization in quantum statistical mechanics
We review some recent developments in the statistical mechanics of isolated
quantum systems. We provide a brief introduction to quantum thermalization,
paying particular attention to the `Eigenstate Thermalization Hypothesis'
(ETH), and the resulting `single-eigenstate statistical mechanics'. We then
focus on a class of systems which fail to quantum thermalize and whose
eigenstates violate the ETH: These are the many-body Anderson localized
systems; their long-time properties are not captured by the conventional
ensembles of quantum statistical mechanics. These systems can locally remember
forever information about their local initial conditions, and are thus of
interest for possibilities of storing quantum information. We discuss key
features of many-body localization (MBL), and review a phenomenology of the MBL
phase. Single-eigenstate statistical mechanics within the MBL phase reveals
dynamically-stable ordered phases, and phase transitions among them, that are
invisible to equilibrium statistical mechanics and can occur at high energy and
low spatial dimensionality where equilibrium ordering is forbidden.Comment: Updated to reflect recent development
Spin-Mediated Consciousness: Theory, Experimental Studies, Further Development & Related Topics
We postulate that consciousness is intrinsically connected to quantum spin
since the latter is the origin of quantum effects in both Bohm and Hestenes
quantum formulisms and a fundamental quantum process associated with the
structure of space-time. Applying these ideas to the particular structures and
dynamics of the brain, we have developed a detailed model of quantum
consciousness. We have also carried out experiments from the perspective of our
theory to test the possibility of quantum-entangling the quantum entities
inside the brain with those of an external chemical substance. We found that
applying magnetic pulses to the brain when an anaesthetic was placed in between
caused the brain to feel the effect of said anaesthetic as if the test subject
had actually inhaled the same. We further found that drinking water exposed to
magnetic pulses, laser light or microwave when an anaesthetic was placed in
between also causes brain effects in various degrees. Additional experiments
indicate that the said brain effect is indeed the consequence of quantum
entanglement. Recently we have studied non-local effects in simple physics
systems. We have found that the pH value, temperature and gravity of a liquid
in the detecting reservoirs can be non-locally affected through manipulating
another liquid in a remote reservoir quantum-entangled with the former. In
particular, the pH value changes in the same direction as that being
manipulated; the temperature can change against that of local environment; and
the gravity can change against local gravity. We suggest that they are mediated
by quantum entanglement between nuclear and/or electron spins in treated liquid
and discuss the profound implications of these results. This paper now also
includes materials on further development of the theory and related topics.Comment: 92 pages; expanded content; minor corrections; for additional
information, please visit http://quantumbrain.or
Black hole holography and mean field evolution
Holographic theories representing black holes are expected to exhibit quantum
chaos. We argue if the laws of quantum mechanics are expected to hold for
observers inside such black holes, then such holographic theories must have a
mean field approximation valid for typical black hole states, and for
timescales approaching the scrambling time. Using simple spin models as
examples, we examine the predictions of such an approach for observers inside
black holes, and more speculatively inside cosmological horizons.Comment: 11 pages, 5 figure
Non-thermalization in trapped atomic ion spin chains
Linear arrays of trapped and laser cooled atomic ions are a versatile
platform for studying emergent phenomena in strongly-interacting many-body
systems. Effective spins are encoded in long-lived electronic levels of each
ion and made to interact through laser mediated optical dipole forces. The
advantages of experiments with cold trapped ions, including high spatiotemporal
resolution, decoupling from the external environment, and control over the
system Hamiltonian, are used to measure quantum effects not always accessible
in natural condensed matter samples. In this review we highlight recent work
using trapped ions to explore a variety of non-ergodic phenomena in long-range
interacting spin-models which are heralded by memory of out-of-equilibrium
initial conditions. We observe long-lived memory in static magnetizations for
quenched many-body localization and prethermalization, while memory is
preserved in the periodic oscillations of a driven discrete time crystal state.Comment: 14 pages, 5 figures, submitted for edition of Phil. Trans. R. Soc. A
on "Breakdown of ergodicity in quantum systems
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