We derive the full linear-response theory for non-relativistic quantum
electrodynamics in the long wavelength limit, show quantum modifications of the
well-known Maxwell's equation in matter and provide a practical framework to
solve the resulting equations by using quantum-electrodynamical
density-functional theory. We highlight how the coupling between quantized
light and matter changes the usual response functions and introduces new types
of cross-correlated light-matter response functions. These cross-correlation

It is well known that the notions of spatial locality are often lost in
quantum systems with long-range interactions, as exhibited by the emergence of
phases with exotic long-range order and faster propagation of quantum
correlations. We demonstrate here that such induced ``quasinonlocal" effects do
not necessarily translate to growth of global entanglement in the quantum
system. By investigating the ground and quenched states of the variable-range,
spin-1/2 Heisenberg Hamiltonian, we observe that the genuine multiparty

Colour centres with long-lived spins are established platforms for quantum
sensing and quantum information applications. Colour centres exist in different
charge states, each of them with distinct optical and spin properties.
Application to quantum technology requires the capability to access and
stabilize charge states for each specific task. Here, we investigate charge
state manipulation of individual silicon vacancies in silicon carbide, a system
which has recently shown a unique combination of long spin coherence time and

We study the subradiant collective states of a periodic chain of two-level
atoms with either transversal or longitudinal transition dipole moments with
respect to the chain axis. We show that long-lived subradiant states can be
obtained for the transversal polarization by properly choosing the chain period
for a given number of atoms in the case of no open diffraction channels. These
highly subradiant states have a linewidth that decreases with the number of

Out-of-time-order correlators (OTOCs) have been proposed as a probe of chaos
in quantum mechanics, on the basis of their short-time exponential growth found
in some particular set-ups. However, it has been seen that this behavior is not
universal. Therefore, we query other quantum chaos manifestations arising from
the OTOCs and we thus study their long-time behavior in systems of completely
different nature: quantum maps, which are the simplest chaotic one-body system

Author(s): Christos N. Gagatsos, Boulat A. Bash, Animesh Datta, Zheshen Zhang, and Saikat Guha
We propose a scheme for covert active sensing using floodlight illumination from a terahertz-bandwidth amplified spontaneous emission (ASE) source and heterodyne detection. We evaluate the quantum-estimation-theoretic performance limit of covert sensing, wherein a transmitter's attempt to sense a ta...
[Phys. Rev. A 99, 062321] Published Tue Jun 18, 2019

Author(s): Alessia Castellini, Bruno Bellomo, Giuseppe Compagno, and Rosario Lo Franco
Quantum information and communication processing within quantum networks usually employ identical particles. Despite this, the physical role of the quantum statistical nature of particles in large-scale networks remains elusive. Here, we show that just the indistinguishability of fermions allows a n...
[Phys. Rev. A 99, 062322] Published Tue Jun 18, 2019

Author(s): Kathleen E. Hamilton, Eugene F. Dumitrescu, and Raphael C. Pooser
In this work we demonstrate experimentally how generative model training can be used as a benchmark for small (fewer than five qubits) quantum devices. Performance is quantified using three data analytic metrics: the Kullback-Leibler divergence and two adaptations of the ${F}_{1}$ score. Using the $...
[Phys. Rev. A 99, 062323] Published Tue Jun 18, 2019

In this report we present a general approach for estimating quantum circuits
by means of measurements. We apply the developed general approach for
estimating the quality of superconducting and optical quantum chips. Using the
methods of quantum states and processes tomography developed in our previous
works, we have defined the adequate models of the states and processes under

We experimentally studied the microwave response of a transmon artificial
atom coupled to two closely spaced resonant modes. When the atom is under
driven with one of the modes, the atom state and mode photons are superposed,
forming the dressed states. Dressed states with 1st, 2nd and 3rd excited states
of the atom were prepared and probed via the strong coupling to the other
resonant mode from the point of view of cavity quantum electrodynamics. The