# All

We provide sufficient conditions on the structure of the interaction

Hamiltonian between a quantum system and the surrounding bath which, without

any external drive or coherent measurements, guarantee the generation of

steady-state coherences (SSC). The SSC this way obtained remarkably turn out to

be independent on the initial state of the system, which therefore could even

be taken initially incoherent. We characterize in detail this phenomenon first

analytically in the weak coupling regime for two paradigmatic models, and then

We present uncertainty relations based on Wigner--Yanase--Dyson skew

information with quantum memory. Uncertainty inequalities both in product and

summation forms are derived. \mbox{It is} shown that the lower bounds contain

two terms: one characterizes the degree of compatibility of two measurements,

and the other is the quantum correlation between the measured system and the

quantum memory. Detailed examples are given for product, separable and

entangled states.

The possible connection between EPR correlations and superluminal

interactions is discussed using simple and palpable arguments. It is shown how

an experiment based on time-like events can allow us to answer the question

"Can a measurement performed on one of the photons of an entangled pair change

the state of the other?" The theorem on superluminal finite-speed causal

influences and superluminal signaling is reexamined. It is shown how

faster-than-light interactions and Lorentz transformations might peacefully

coexist.

Quantum mechanics allows measurements that surpass the fundamental

sensitivity limits of classical methods. To benefit from the quantum advantage

in a practical setting, the receiver should use communication channels

resources optimally; this can be done employing large communication alphabets.

Here we show the fundamental sensitivity potential of a quantum receiver for

coherent communication with frequency shift keying. We introduce an adaptive

quantum protocol for this receiver, show that its sensitivity outperforms other

Interference experiments provide a simple yet powerful tool to unravel

fundamental features of quantum physics. Here we engineer an RF-driven,

time-dependent bilinear coupling that can be tuned to implement a robust 50:50

beamsplitter between stationary states stored in two superconducting cavities

in a three-dimensional architecture. With this, we realize high contrast

Hong-Ou- Mandel (HOM) interference between two spectrally-detuned stationary

modes. We demonstrate that this coupling provides an efficient method for

We introduce the first complete and approximatively universal diagrammatic

language for quantum mechanics. We make the ZX-Calculus, a diagrammatic

language introduced by Coecke and Duncan, complete for the so-called Clifford+T

quantum mechanics by adding four new axioms to the language. The completeness

of the ZX-Calculus for Clifford+T quantum mechanics was one of the main open

questions in categorical quantum mechanics. We prove the completeness of the

We consider a general open system dynamics and we provide a recursive method

to derive the associated non-Markovian master equation in a perturbative

series. The approach relies on a momenta expansion of the open system

evolution. Unlike previous perturbative approaches of this kind, the method

presented in this paper provides a recursive definition of each perturbative

term. Furthermore, we give an intuitive diagrammatic description of each term

of the series, which pro- vides an useful analytical tool to build them and to

Recently, Rydberg atoms appeared as a viable alternative to the quantum gates

built on atomic or molecular ions. The lifetimes of the circular Rydberg states

can be in the millisecond range. That prevents inherent metastability of the

Rydberg atoms to influence computation at the typical decoherence times, which

are now being achieved in the range of 1 ms. The paper proposes to use a

pinning potential of an image charge on a cryogenic substrate (liquid He, in

There is recent interest in determining energy costs of shortcuts to

adiabaticity (STA), but different definitions of "cost" have been used. We

demonstrate the importance of taking into account the Control System (CS) for a

fair assessment of energy flows and consumptions. Models where the primary

system subjected to the shortcut and the CS can be examined explicitly help to

suggest, clarify, and test general principles, in particular the crucial

importance of the CS. We model the energy consumption and power to transport an

We show that for any collection of hermitian operators A1...An , and any

quantum state there is a unique joint distribution on R^n, with the property

that the marginals of all linear combinations of the operators coincide with

their quantum counterpart. We call it the Wigner distribution, because for

position and momentum this property defines the standard Wigner function. In

this note we discuss the application to finite dimensional systems, establish