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Devices relying on microwave circuitry form a cornerstone of many classical
and emerging quantum technologies. A capability to provide in-situ, noninvasive
and direct imaging of the microwave fields above such devices would be a
powerful tool for their function and failure analysis. In this work, we build
on recent achievements in magnetometry using ensembles of nitrogen vacancy
centres in diamond, to present a widefield microwave microscope with few-micron

In-principle restrictions on the amount of information that can be gathered
about a system have been proposed as a foundational principle in several recent
reconstructions of the formalism of quantum mechanics. However, it seems
unclear precisely why one should be thus restricted. We investigate the notion
of paradoxical self-reference as a possible origin of such epistemic horizons
by means of a fixed-point theorem in Cartesian closed categories due to F. W.
Lawvere that illuminates and unifies the different perspectives on

Multiparticle entangled states, essential ingredients for modern quantum
technologies, are routinely generated in experiments of atomic Bose-Einstein
condensates (BECs). However, the entanglement in ultracold interacting Fermi
gases has not been yet exploited. In this work, by using an ansatz of composite
bosons, we show that many-particle entanglement between two fermionic ensembles
localized in spatially separated modes can be generated by splitting an
ultracold interacting Fermi gas in the (molecular) BEC regime. This

Photon-number squeezing and correlations enable measurement of absorption
with an accuracy exceeding that of the shot-noise limit. However, sub-shot
noise imaging and sensing based on these methods require high detection
efficiency, which can be a serious obstacle if measurements are carried out in
"difficult" spectral ranges. We show that this problem can be overcome through
the phase-sensitive amplification before detection. Here we propose an
experimental scheme of sub-shot-noise imaging with tolerance to detection

The second half of this essay tells the story of the genesis and early
development of the notion of black hole entropy, in the style of an after
dinner talk (apart from a long technical footnote). The first half sketches the
development of the concept of entropy, beginning with Carnot, passing via
Thomson, Clausius, Boltzmann, Planck, von Neumann, and Shannon on the way to
Bekenstein, and the essay ends with a retrospective on Lema\^itre. The central
theme is the fault-tolerant way that profound insights have emerged from simple

General nonequilibrium quantum transport equations are derived for a coupled
system of charge carriers, Dirac spin, isospin (or valley spin), and
pseudospin, such as either one of the band, layer, impurity, and boundary
pseudospins. Limiting cases are obtained for one, two or three different kinds
of spin ocurring in a system. We show that a characteristic integer number
N_{s} determines the formal form of spin quantum transport equations,
irrespective of the type of spins or pseudospins, as well as the maximal

In this note we discuss the geometry of matrix product states with periodic
boundary conditions and provide three infinite sequences of examples where the
quantum max-flow is strictly less than the quantum min-cut. In the first we fix
the underlying graph to be a 4-cycle and verify a prediction of Hastings that
inequality occurs for infinitely many bond dimensions. In the second we
generalize this result to a 2d-cycle. In the third we show that the 2d-cycle

We investigate quantum sensing of rotation with a multi-atom Sagnac
interferometer and present multi-partite entangled states to enhance the
sensitivity of rotation frequency. For studying the sensitivity, we first
present a Hermitian generator with respect to the rotation frequency. The
generator, which contains the Sagnac phase, is a linear superposition of a z
component of the collective spin and a quadrature operator of collective bosons
depicting the trapping modes, which enables us to conveniently study the

Quantum emitters interacting with two-dimensional photonic-crystal baths
experience strong and anisotropic collective dissipation when they are
spectrally tuned to 2D Van-Hove singularities. In this work, we show how to
turn this dissipation into coherent dipole-dipole interactions with tuneable
range by breaking the lattice degeneracy at the Van-Hove point with a
superlattice geometry. Using a coupled-mode description, we show that the
origin of these interactions stems from the emergence of a qubit-photon bound

Providing the microscopic behavior of a thermalization process has always
been an intriguing issue. There are several models of thermalization, which
often requires interaction of the system under consideration with the
microscopic constituents of the macroscopic heat bath. With an aim to simulate
such a thermalization process, here we look at the thermalization of a
two-level quantum system under the action of a Markovian master equation
corresponding to memory-less action of a heat bath, kept at a certain