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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

- Read more about Hardware for Dynamic Quantum Computing. (arXiv:1704.08314v1 [quant-ph])
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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.