Quantum memory, capable of stopping flying photons and storing their quantum
coherence, is essential for scalable quantum technologies. A broadband quantum
memory operating at room temperature will enable building large-scale quantum
systems for real-life applications, for instance, high-speed quantum repeater
for long-distance quantum communication and synchronised multi-photon quantum
sources for quantum computing and quantum simulation. Albeit advances of
pushing bandwidth from narrowband to broadband and storage media from

We show that the physical mechanism for the equilibration of closed quantum
systems is dephasing, and identify the energy scales that determine the
equilibration timescale of a given observable. For realistic physical systems
(e.g those with local Hamiltonians), our arguments imply timescales that do not
increase with the system size, in contrast to previously known upper bounds. In
particular, we show that, for such Hamiltonians, the matrix representation of

We study an accumulation mode Si/SiGe double quantum dot (DQD) containing a
single electron that is dipole coupled to microwave photons in a
superconducting cavity. Measurements of the cavity transmission reveal
dispersive features due to the DQD valley states in Si. The occupation of the
valley states can be increased by raising temperature or applying a finite
source-drain bias across the DQD, resulting in an increased signal. Using
cavity input-output theory and a four-level model of the DQD, it is possible to

Refocalization sequences in Nuclear Magnetic Resonance (NMR) can in principle
reverse the coherent evolution under the secular dipolar Hamiltonian of a
closed system. We use this experimental strategy to study the effect of
irreversible decoherence on the signal amplitude attenuation in a single
crystal hydrated salt where the nuclear spin system consists in the set of
hydration water proton spins having a strong coupling within each pair and a
much weaker coupling with other pairs. We study the experimental response of

Reichenbach's principle asserts that if two observed variables are found to
be correlated, then there should be a causal explanation of these correlations.
Furthermore, if the explanation is in terms of a common cause, then the
conditional probability distribution over the variables given the complete
common cause should factorize. The principle is generalized by the formalism of
causal models, in which the causal relationships among variables constrain the

In quantum information W states are a central class of multipartite entangled
states because of their robustness against noise and use in many quantum
processes. Their generation however remains a demanding task whose difficulty
increases with the number of particles. We report a simple scalable conceptual
scheme where a single particle in an ancilla mode works as entanglement
catalyst of W state for other $N$ separated identical particles. A crucial
novel aspect of the scheme, which exploits basically spatial

We give a quantum algorithm for solving semidefinite programs (SDPs). It has
worst case running time n^{1/2}m^{1/2}s poly(log(n), log(m), R, r, 1/delta),
with n and s the dimension and sparsity of the input matrices, respectively, m
the number of constraints, delta the accuracy of the solution, and R, r upper
bounds on the size of the optimal primal and dual solutions. This gives a
square-root unconditional speed-up over any classical method for solving SDPs

Starting from an idea of S.L. Adler~\cite{Adler2015}, we develop a novel
model of gravity-induced spontaneous wave-function collapse. The collapse is
driven by complex stochastic fluctuations of the spacetime metric. After having
derived the fundamental equations, we prove the collapse and amplification
mechanism, the two most important features of a consistent collapse model.
Under reasonable simplifying assumptions, we constrain the strength $\xi$ of

Even the quantum simulation of simple molecules such as Fe$_2$S$_2$ requires
more than 10$^6$ qubits. In order to assess such a multimillion scale of
identical qubits and control lines, the silicon platform seems to be one of the
most indicated routes as it provides the capability of nanometric, serial and
industrial quality fabrication. The maximum amount of quantum information per
unit surface and the consequent space constraints on qubit operations are key

We compare quantum dynamics in the presence of Markovian dephasing for a
particle hopping on a chain and for an Ising domain wall whose motion leaves
behind a string of flipped spins. Exact solutions show that on an infinite
chain, the transport responses of the models are nearly identical. However, on
finite-length chains, the broadening of discrete spectral lines is much more
noticeable in the case of a domain wall.