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The eigenstate thermalization hypothesis (ETH) and the theory of linear
response (LRT) are celebrated cornerstones of our understanding of the physics
of many-body quantum systems out of equilibrium. While the ETH provides a
generic mechanism of thermalization for states arbitrarily far from
equilibrium, LRT extends the successful concepts of statistical mechanics to
situations close to equilibrium. In our work, we connect these cornerstones to
shed light on the route to equilibrium for a class of properly prepared states.

A non-Hermitian topological insulator is fundamentally different from
conventional topological insulators. The non-Hermitian skin effect arises in a
nonreciprocal tight binding lattice with open edges. In this case, not only
topological states but also bulk states are localized around the edges of the
nonreciprocal system. We discuss that controllable switching from topological
edge states into topological extended states in a chiral symmetric
non-Hermitian system is possible. We show that the skin depth decreases with

Various quantum applications can be reduced to estimating expectation values,
which are inevitably deviated by operational and environmental errors. Although
errors can be tackled by quantum error correction, the overheads are far from
being affordable for near-term technologies. To alleviate the detrimental
effects of errors, quantum error mitigation techniques have been proposed,
which require no additional qubit resources. Here, we benchmark the performance
of a quantum error mitigation technique based on probabilistic error

Photonic hyper-crystals combine the most interesting features of hyperbolic
metamaterials and photonic crystals. Since the dispersion law of extraordinary
photons in hyperbolic metamaterials does not exhibit the usual diffraction
limit, photonic hyper-crystals exhibit light localization on deep subwavelength
scales, leading to considerable enhancement of nonlinear photon-photon
interaction. Therefore, similar to their conventional photonic crystal
counterparts, nonlinear photonic hyper-crystals appear to be very promising in

We derive an effective Dicke model in momentum space to describe collective
effects in the quantum regime of a free-electron laser (FEL). The resulting
exponential gain from a single passage of electrons allows the operation of a
Quantum FEL in the high-gain mode and avoids the experimental challenges of an
X-ray FEL oscillator. Moreover, we study the intensity fluctuations of the
emitted radiation which turn out to be super-Poissonian.

Qubit, operator and gate resources required for the digitization of lattice
$\lambda\phi^4$ scalar field theories onto quantum computers are considered,
building upon the foundational work by Jordan, Lee and Preskill, with a focus
towards noisy intermediate-scale quantum (NISQ) devices. The Nyquist-Shannon
sampling theorem, introduced in this context by Macridin, Spentzouris, Amundson
and Harnik building on the work of Somma, provides a guide with which to

Networking plays a ubiquitous role in quantum technology. It is an integral
part of quantum communication and has significant potential for upscaling
quantum computer technologies that are otherwise not scalable. Recently, it was
realized that sensing of multiple spatially distributed parameters may also
benefit from an entangled quantum network. Here we experimentally demonstrate
how sensing of an averaged phase shift among four distributed nodes benefits
from an entangled quantum network. Using a four-mode entangled continuous

The decoy-state method has been developed rapidly in quantum key distribution
(QKD) since it is immune to photon-number splitting attacks. However, two basis
detector efficiency asymmetry, which exists in realistic scenarios, has been
ignored in the prior results. By using the recent 4-intensity decoy-state
optimization protocol, we report the first implementation of high-rate QKD with
asymmetric basis detector efficiency, demonstrating 1.9 to 33.2 times higher

We show that detection of single photons is not subject to the fundamental
limitations that accompany quantum linear amplification of bosonic mode
amplitudes, even though a photodetector does amplify a few-photon input signal
to a macroscopic output signal. Alternative limits are derived for
\emph{nonlinear} photon-number amplification schemes with optimistic
implications for single-photon detection. Four commutator-preserving
transformations are presented: one idealized (which is optimal) and three more

We propose a profound consequence of symmetry towards the axiomatic
derivation of Hilbert space quantum theory. Specifically, we show that the
symmetry of information gain in minimal error state discrimination induces a
non-trivial proviso on the state space structure of a physical theory. The
symmetry considered here puts a restriction on the means of optimal guessing of
a system's state from that of an ensemble. We coin the term information
symmetry (IS) since it constrains the way optimal information gain occurs in

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