554 research outputs found
Non-stationary coherent quantum many-body dynamics through dissipation
The assumption that quantum systems relax to a stationary state in the
long-time limit underpins statistical physics and much of our intuitive
understanding of scientific phenomena. For isolated systems this follows from
the eigenstate thermalization hypothesis. When an environment is present the
expectation is that all of phase space is explored, eventually leading to
stationarity. Notable exceptions are decoherence-free subspaces that have
important implications for quantum technologies and have so far only been
studied for systems with a few degrees of freedom. Here we identify simple and
generic conditions for dissipation to prevent a quantum many-body system from
ever reaching a stationary state. We go beyond dissipative quantum state
engineering approaches towards controllable long-time non-stationarity
typically associated with macroscopic complex systems. This coherent and
oscillatory evolution constitutes a dissipative version of a quantum
time-crystal. We discuss the possibility of engineering such complex dynamics
with fermionic ultracold atoms in optical lattices.Comment: Main text in MS Word (10 pages, 4 figures) and Supplementary material
in TeX (10 pages, 2 figures). Main text PDF embedded in TeX. Version as
accepted by Nature Communication
Quantum network teleportation for quantum information distribution and concentration
We investigate the schemes of quantum network teleportation for quantum
information distribution and concentration which are essential in quantum cloud
computation and quantum internet. In those schemes, the cloud can send
simultaneously identical unknown quantum states to clients located in different
places by a network like teleportation with a prior shared multipartite
entangled state resource. The cloud first perform the quantum operation, each
client can recover their quantum state locally by using the classical
information announced by the cloud about the measurement result. The number of
clients can be beyond the number of identical quantum states intentionally
being sent, this quantum network teleportation can make sure that the retrieved
quantum state is optimal. Furthermore, we present a scheme to realize its
reverse process, which concentrates the states from the clients to reconstruct
the original state of the cloud. These schemes facilitate the quantum
information distribution and concentration in quantum networks in the framework
of quantum cloud computation. Potential applications in time synchronization
are discussed.Comment: 7 pages, 1 figur
Parsing a sequence of qubits
We develop a theoretical framework for frame synchronization, also known as
block synchronization, in the quantum domain which makes it possible to attach
classical and quantum metadata to quantum information over a noisy channel even
when the information source and sink are frame-wise asynchronous. This
eliminates the need of frame synchronization at the hardware level and allows
for parsing qubit sequences during quantum information processing. Our
framework exploits binary constant-weight codes that are self-synchronizing.
Possible applications may include asynchronous quantum communication such as a
self-synchronizing quantum network where one can hop into the channel at any
time, catch the next coming quantum information with a label indicating the
sender, and reply by routing her quantum information with control qubits for
quantum switches all without assuming prior frame synchronization between
users.Comment: 11 pages, 2 figures, 1 table. Final accepted version for publication
in the IEEE Transactions on Information Theor
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