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We present an in-depth study of the non-equilibrium statistics of the
irreversible work produced during sudden quenches in proximity of the
structural linear-zigzag transition of ion Coulomb crystals in 1+1 dimensions.
By employing both an analytical approach based on a harmonic expansion and
numerical simulations, we show the divergence of the average irreversible work
in proximity of the transition. We show that the non-analytic behaviour of the
work fluctuations can be characterized in terms of the critical exponents of

We construct $d\times d$ dimensional bound entangled states, which violate
for any $d>2$ a bipartite Bell inequality introduced in this paper. We
conjecture that the proposed class of Bell inequalities act as dimension
witnesses for bound entangled states: for any $d>2$, there exists a Bell
inequality from this class, which can be violated with bound entangled states
only if their Hilbert space dimension is at least $d\times d$. Numerics
supports this conjecture up to $d=8$.

We analyze correlations between pairs of particle detectors quadratically
coupled to a real scalar field. We find that, while a single quadratically
coupled detector presents no divergences, when one considers pairs of detectors
there emerge unanticipated persistent divergences (not regularizable via smooth
switching or smearing) in the entanglement they acquire from the field. We have
characterized such divergences, discussed whether a suitable regularization can

Tower of States analysis is a powerful tool for investigating phase
transitions in condensed matter systems. Spontaneous symmetry breaking implies
a specific structure of the energy eigenvalues and their corresponding quantum
numbers on finite systems. In these lecture notes we explain the group
representation theory used to derive the spectral structure for several
scenarios of symmetry breaking. We give numerous examples to compute quantum
numbers of the degenerate groundstates, including translational symmetry

An exact reduced dynamical map along with its operator sum representation is
derived for a central spin interacting with a thermal spin environment. The
dynamics of the central spin shows high sustainability of quantum traits like
coherence and entanglement in the low temperature regime. However, for
sufficiently high temperature and when the number of bath particles approaches
the thermodynamic limit, this feature vanishes and the dynamics closely mimics

We provide a new way to bound the security of quantum key distribution using
only the diagrammatic behavior of complementary observables and essential
uniqueness of purification for quantum channels. We begin by demonstrating a
proof in the simplest case, where the eavesdropper doesn't noticeably disturb
the channel at all and has no quantum memory. We then show how this case
extends with almost no effort to account for quantum memory and noise.

We describe the hardware, gateware, and software developed at Raytheon BBN
Technologies for dynamic quantum information processing experiments on
superconducting qubits. In dynamic experiments, real-time qubit state
information is fedback or fedforward within a fraction of the qubits' coherence
time to dynamically change the implemented sequence. The hardware presented
here covers both control and readout of superconducting qubits. For readout we
created a custom signal processing gateware and software stack on commercial

Quantum computing is moving rapidly to the point of deployment of technology.
Functional quantum devices will require the ability to correct error in order
to be scalable and effective. A leading choice of error correction, in
particular for modular or distributed architectures, is the surface code with
logical two-qubit operations realised via "lattice surgery". These operations
consist of "merges" and "splits" acting non-unitarily on the logical states and

We study the performance of a single qubit-laser as a quantum sensor to
measure the amplitude and phase of a driving field. By using parameter
estimation theory we show that certain suitable field quadratures are optimal
observables in the lasing phase. The quantum Fisher information scales linearly
with the number of bosons and thus the precision can be enhanced by increasing
the incoherent pumping acting on the qubit. If we restrict ourselves to
measurements of the boson number observable, then the optimal operating point

Here we study the possibilities of creating a bad cavity laser on forbidden
transition in cold ions forming large Coulomb crystal in linear Paul trap. We
consider micromotion-induced shifts and coupling strengths, and perform
quantitative estimations of the attainable laser power for lasing on the
${^3D_2} \rightarrow {^1S_0}$ transition in ${\rm ^{176}Lu^+}$ ions in a
spherical-symmetric trap.