The quantum coherence and gate fidelity of electron spin qubits in
semiconductors is often limited by noise arising from coupling to a bath of
nuclear spins. Isotopic enrichment of spin-zero nuclei such as $^{28}$Si has
led to spectacular improvements of the dephasing time $T_2^*$ which,
surprisingly, can extend two orders of magnitude beyond theoretical
expectations. Using a single-atom $^{31}$P qubit in enriched $^{28}$Si, we show
that the abnormally long $T_2^*$ is due to the controllable freezing of the

Starting from a geometric perspective, we derive a quantum speed limit for
arbitrary open quantum evolution, which could be Markovian or non-Markovian,
providing a fundamental bound on the time taken for the most general quantum
dynamics. Our methods rely on measuring angles and distances between (mixed)
states represented as generalized Bloch vectors. We study the properties of our
bound and present its form for closed and open evolution, with the latter in

We present a system of equations and an explicit solution for the problem of
determining the MaxEnt state of a quantum system satisfying symmetry

We resolve phonon number states in the spectrum of a superconducting qubit
coupled to a multimode acoustic cavity. Crucial to this resolution is the sharp
frequency dependence in the qubit-phonon interaction engineered by coupling the
qubit to surface acoustic waves in two locations separated by $\sim40$ acoustic
wavelengths. In analogy to double-slit diffraction, the resulting
self-interference generates high-contrast frequency structure in the
qubit-phonon interaction. We observe this frequency structure both in the

In contrast with classical physics, in quantum physics some sets of
measurements are incompatible in the sense that they can not be performed
simultaneously. Among other applications, incompatibility allows for
contextuality and Bell nonlocality. This makes of crucial importance developing
tools for certifying whether a set of measurements posses a certain structure
of incompatibility. Here we show that, for quantum or nonsignaling models, if
the measurements employed in a Bell test satisfy a given type of compatibility,

We explore an intriguing alternative for a fast and high-fidelity generation
of steady-state entanglement. By exponentially enhancing the atom-cavity
interaction, we obtain an exponentially-enhanced effective cooperativity of the
system, which results in a high fidelity of the state generation. Meanwhile, we
modulate the amplitudes of the driving fields to accelerate the population
transfer to a target state, e.g., a Bell state. An exponentially-shortened

Via the hierarchy of correlations, we study the Mott insulator phase of the
Fermi-Hubbard model in the limit of strong interactions and derive a quantum
Boltzmann equation describing its relaxation dynamics. In stark contrast to the
weakly interacting case, we find that the scattering cross sections strongly
depend on the momenta of the colliding quasi-particles and holes. Therefore,
the relaxation towards equilibrium crucially depends on the spectrum of

The possibility to exploit quantum coherence to strongly enhance the
efficiency of charge transport in solid state devices working at ambient
conditions would pave the way to disruptive technological applications. In this
work, we tackle the problem of the quantum transport of photogenerated
electronic excitations subject to dephasing and on-site Coulomb interactions.
We show that the transport to a continuum of states representing metallic
collectors can be optimized by exploiting the "superradiance" phenomena. We

We study a quantum dot coupled to two semiconducting reservoirs, when the dot
level and the electrochemical potential are both close to a band edge in the
reservoirs. This is modelled with an exactly solvable Hamiltonian without
interactions (the Fano-Anderson model). The model is known to show an abrupt
transition as the dot-reservoir coupling is increased into the strong-coupling
regime for a broad class of band structures. This transition involves an

Quantum algorithms are usually described as monolithic circuits, becoming
large at modest input size. Near-term quantum architectures can only manage a
small number of qubits. We develop an automated method to distribute quantum
circuits over multiple agents, minimising quantum communication between them.
We reduce the problem to hypergraph partitioning and then solve it with
state-of-the-art optimisers. This makes our approach useful in practice, unlike