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.

# All

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