Irreversibility in quantum measurements shares conceptual links with statistical and thermodynamical irreversibility. Here, the authors are able to operationally associate an "arrow of time” to quantum weak measurements, testing it experimentally on a cloud of ultracold atoms.
More than a century after it took the first steps, quantum mechanics is now living a second youth, mainly due to the growing efforts in exploiting inherently quantum advantages for technological applications. At the same time, more fundamentally-oriented research is still storming the citadel of quantum weirdness and paradoxes. In this page, we highlight research papers in quantum-related areas.
Most demonstrations of quantum advantages with optics rely on single photons, and are thus difficult to scale up. Here, the authors use coherent states to demonstrate a quantum advantage for the task of verifying the solution to a NP-complete problem when only partial information on the solution is available.
The Gibbs paradox stems from the entropy change upon mixing two gases. Here, by considering bosonic and fermionic statistics, the authors show that an observer unable to distinguish the particles’ spins assigns a greater entropy increase to the mixing process than is possible in classical physics.
The quantum marginal problem interrogates the existence of a global pure quantum state with some given marginals. Here, the authors reformulate it as an optimisation problem, and specifically as the existence of a two-party separable state with additional semidefinite constraints.
Scaling advantage over path-integral Monte Carlo in quantum simulation of geometrically frustrated magnets
Experimental demonstration of quantum speedup that scales with the system size is the goal of near-term quantum computing. Here, the authors demonstrate such scaling advantage for a D-Wave quantum annealer over analogous classical algorithms in simulations of frustrated quantum magnets.
Suitability for large-scale quantum computation imposes severe requirements on single-photon sources in terms of purity, indistinguishability and heralding efficiency. Here, the authors boost all these figures of merit through a dual-mode pump-delayed four-wave mixing scheme in low-loss silicon waveguides.
Individually addressed rare earth atoms in solid crystals are an emerging platform for quantum information processing. Here the authors demonstrate a key requirement, by realizing single-shot, quantum non-demolition measurements of the spin of single Er3+ ions in Y2SiO5 crystals with nearly 95% fidelity.
Experimental studies of topological phenomena for interacting quantum systems are challenging. Here, the authors exploit the analogy between a quantum two-body problem in one dimension and a classical two-dimensional problem, emulating two-photon topological bound states in 1D using a 2D electrical circuit.
It’s still unclear whether entanglement can be generated, survive, and be observed in hot environments dominated by random collisions. Here, the authors use quantum non-demolition measurement on a hot alkali vapor to put more than ten trillion atoms in a long-lived and spatially extended entangled state.
Photonic quantum computation via bulk optical nonlinearities presents challenges, due to the weakness of nonlinearity and the difficulties in doing without feed-forward control. Here, the authors propose an all-unitary approach that is based on a triply-resonant cavity with a time-dependent drive.
Conditional quantum operation of two exchange-coupled single-donor spin qubits in a MOS-compatible silicon device
Operating donor-based quantum computers in silicon is hindered by the dependence of inter-qubit coupling on the precise donor position. Here, the authors show controlled rotation operation on exchange-coupled electron spins in the weak-exchange regime, loosening the requirements on positioning precision.
It is hard to design quantum neural networks able to work with quantum data. Here, the authors propose a noise-robust architecture for a feedforward quantum neural network, with qudits as neurons and arbitrary unitary operations as perceptrons, whose training procedure is efficient in the number of layers.
The no-signaling principle constrains which multipartite correlations are allowed, but network scenarios considered so far were limited to specific cases. Here, the authors apply inflation technique to the no-input/binary-output triangle network, and show that it admits non-trilocal distributions.
Despite recent demonstrations of coherent spin-state transfer in arrays of spin qubits via exchange interaction, all-matter spin-state teleportation is still out of reach. Here the authors provide evidence for conditional teleportation of quantum-dot spin states, entanglement swapping, and gate teleportation.
While continuous-variable QKD presents many experimental advantages, a full security proof that addresses the most general attacks and digitized signals in the finite-size regime has so far been lacking. Here, the authors fill this gap in the case of a protocol with a binary phase modulation.