19 research outputs found
Nonreciprocal Amplification Transition in a Driven-Dissipative Quantum Network
We study the transport properties of a driven-dissipative quantum network,
where multiple bosonic cavities such as photonic microcavities are coupled
through a nonreciprocal bus with unidirectional transmission. For short-range
coupling between the cavities, the occurrence of nonreciprocal amplification
can be linked to a topological phase transition of the underlying dynamic
Hamiltonian. However, for long-range coupling, we find that the nonreciprocal
amplification transition deviates drastically from the topological phase
transition. Nonetheless, we show that the nonreciprocal amplification
transition can be connected to the emergence of zero-energy edge states of an
auxiliary Hamiltonian with chiral symmetry even in the long-range coupling
limit. We also investigate the stability, the crossover from short to
long-range coupling, and the bandwidth of the nonreciprocal amplification. Our
work has potential application in signal transmission and amplification, and
also opens a window to non-Hermitian systems with long-range coupling and
nontrivial boundary effects.Comment: 5 pages, 4 figure
Observation of Topological Weyl Type I-II Transition in Synthetic Mechanical Lattices
Weyl points are three-dimensional linear points between bands that exhibit
unique stability to perturbations and are accompanied by topologically
non-trivial surface states. However, the discovery and control of Weyl points
in nature poses significant challenges. While recent advances have allowed for
engineering Weyl points in photonic crystals and metamaterials, the topological
transition between Weyl semimetals with distinct types of Weyl points remains
yet to be reported. Here, exploiting the flexible measurement-feedback control
of synthetic mechanical systems, we experimentally simulate Weyl semimetals and
observe for the first time the transition between states with type-I and
type-II Weyl points. We directly observe the change in the band structures
accompanying the transition and identify the Fermi arc surface states
connecting the Weyl points. Further, making use of the non-reciprocal feedback
control, we demonstrate that the introduction of non-Hermiticity significantly
impacts the topological transition point, as well as the edge localization of
the Fermi arc surface states. Our findings offer valuable insights into the
design and realization of Weyl points in mechanical systems, providing a
promising avenue for exploring novel topological phenomena in non-Hermitian
physics
Tutorial: Nonlinear magnonics
Nonlinear magnonics studies the nonlinear interaction between magnons and
other physical platforms (phonon, photon, qubit, spin texture) to generate
novel magnon states for information processing. In this tutorial, we first
introduce the nonlinear interactions of magnons in pure magnetic systems and
hybrid magnon-phonon and magnon-photon systems. Then we show how these
nonlinear interactions can generate exotic magnonic phenomena. In the classical
regime, we will cover the parametric excitation of magnons, bistability and
multistability, and the magnonic frequency comb. In the quantum regime, we will
discuss the single magnon state, Schr\"{o}dinger cat state and the entanglement
and quantum steering among magnons, photons and phonons. The applications of
the hybrid magnonics systems in quantum transducer and sensing will also be
presented. Finally, we outlook the future development direction of nonlinear
magnonics.Comment: 50 pages, 26 figure
Remote preparation of optical cat states based on Gaussian entanglement
Remote state preparation enables one to prepare and manipulate quantum state
non-locally. As an essential quantum resource, optical cat state is usually
prepared locally by subtracting photons from a squeezed vacuum state. For
remote quantum information processing, it is essential to prepare and
manipulate optical cat states remotely based on Gaussian entanglement, which
remains a challenge. Here, we present experimental preparation of optical cat
states based on a remotely distributed two-mode Gaussian entangled state in a
lossy channel. By performing photon subtraction and homodyne projective
measurement at Alice's station, an optical cat state is prepared remotely at
Bob's station. Furthermore, the prepared cat state is rotated by changing
Alice's measurement basis of homodyne detection, which demonstrates the remote
manipulation of it. By distributing two modes of the two-mode Gaussian
entangled state in lossy channels, we demonstrate that the remotely prepared
cat state can tolerate much more loss in Alice's channel than that in Bob's
channel. We also show that cat states with amplitudes larger than 2 can be
prepared by increasing the squeezing level and subtracting photon numbers. Our
results make a crucial step toward remote hybrid quantum information processing
involving discrete- and continuous-variable techniques
Correlation-pattern-based Continuous-variable Entanglement Detection through Neural Networks
Entanglement in continuous-variable non-Gaussian states provides
irreplaceable advantages in many quantum information tasks. However, the sheer
amount of information in such states grows exponentially and makes a full
characterization impossible. Here, we develop a neural network that allows us
to use correlation patterns to effectively detect continuous-variable
entanglement through homodyne detection. Using a recently defined stellar
hierarchy to rank the states used for training, our algorithm works not only on
any kind of Gaussian state but also on a whole class of experimentally
achievable non-Gaussian states, including photon-subtracted states. With the
same limited amount of data, our method provides higher accuracy than usual
methods to detect entanglement based on maximum-likelihood tomography.
Moreover, in order to visualize the effect of the neural network, we employ a
dimension reduction algorithm on the patterns. This shows that a clear boundary
appears between the entangled states and others after the neural network
processing. In addition, these techniques allow us to compare different
entanglement witnesses and understand their working. Our findings provide a new
approach for experimental detection of continuous-variable quantum correlations
without resorting to a full tomography of the state and confirm the exciting
potential of neural networks in quantum information processing.Comment: 9 pages (incl. appendix), 6 figures, comments welcome