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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

- Read more about Quantum common causes and quantum causal models. (arXiv:1609.09487v2 [quant-ph] UPDATED)
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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

- Read more about Gravity induced Wave Function Collapse. (arXiv:1701.02236v3 [quant-ph] UPDATED)
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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.