Given a renormalization scheme, we show how to formulate tractable convex relaxation of the set feasible local density matrices many-body quantum system. The is obtained by introducing hierarchy constraints between reduced states ever-growing sets lattice sites. coarse-graining maps underlying procedure serve eliminate vast number those constraints, such that remaining ones can be enforced with reasonable computational means. This process used obtain rigorous lower bounds on ground-state...

We propose a method to produce fast transitionless dynamics for finite-dimensional quantum systems without requiring additional Hamiltonian components not included in the initial control setup, remaining close true adiabatic path at all times. The strategy is based on introduction of an effective counterdiabatic scheme: correcting constructed which approximatively cancels nonadiabatic effects, inducing evolution tracking states closely. This can be absorbed into by adding oscillation...

One of the most widespread methods to determine if a quantum state is entangled, or quantify its entanglement dimensionality, by measuring fidelity with respect pure state. In this Letter, we find large class states whose cannot be detected in manner; call them unfaithful. We that unfaithful are ubiquitous information theory. For small dimensions, check numerically bipartite both entangled and Similarly, numerical searches low dimensions show remain but become when certain amount white noise...

We present a universal mechanism that, acting on any target qubit, propagates it to the state had T time units before experiment started. This protocol works by setting superposition of flight paths, where is acted uncharacterized, but repeatable, quantum operations. Independently effect each these individual operations target, successful interference paths causes leap its past state. prove for generic interaction effects, will herald rewinding with probability 1 after some finite number steps.

In quantum mechanics, the unitary nature of time evolution makes it intrinsically reversible, given control over system in question. Remarkably, there have been several recent demonstrations protocols for reverting unknown unitaries scenarios where even interactions with target are unknown. These limited by their probabilistic nature, raising fundamental question whether time-reversal could be performed deterministically. Here we show that physics indeed allows this exploiting non-commuting...

We introduce a method to speed up adiabatic protocols for creating entanglement between two qubits dispersively coupled transmission line, while keeping fidelities high and maintaining robustness control errors. The takes genuinely sweeps, ranging from simple Landau-Zener drive boundary cancellation methods local drivings, adds fast oscillations the protocol canceling unwanted transitions. compare our with existing in state-of-the-art parameter range show substantial gains. Numerical...

The simulation of quantum systems has been a key aim technologies for decades, and the generalisation to open is necessary include physically realistic systems. We introduce an approach simulations system dynamics in terms environment minimal size time-dependent Hamiltonian. This enables implementation continuous-time with finite environment, whereas state art methods require infinite or only match at discrete times. find sufficient conditions this Hamiltonian be well behaved and, when these...

We show that there exist non-relativistic scattering experiments which, if successful, freeze out, speed up or even reverse the free dynamics of any ensemble quantum systems present in region. This time translation effect is universal, i.e., it independent particular interaction between particles and target systems, (possibly non-Hermitian) Hamiltonian governing evolution latter. The protocols require careful preparation probes which are scattered, success heralded by projective measurements...

Quantum simulators, machines that can replicate the dynamics of quantum systems, are being built as useful devices and seen a stepping stone to universal computers. A key difference between two is computers have ability perform logic gates make up algorithms. We propose method for learning how construct these efficiently by using simulator optimal control on itself. This bypasses major problems purely classical approaches problem: need an accurate model system, computer more powerful than...

We investigate the problem of what evolutions an open quantum system described by a time-local Master equation can undergo with universal coherent controls. A series conditions are given which exclude channels from being reachable any unitary controls, assuming that coupling to environment is not modified. These primarily arise defining decay rates for generator dynamics system, and then showing controlling only make these more isotropic. This forms constraints on shape non-unitality allowed...

Current protocols to revert time evolutions of quantum systems suffer either from low success probabilities, or not being universal - they require knowledge about the evolving state, its evolution, interaction through which evolution is reverted. We overcome these limitations, and demonstrate a novel time-reversal protocol by implementing it on photonic platform using SWITCH. The schemes universality verified clear advantage with respect optimal classical stragegy shown running large...

The authors construct a coherence certifier derived from simple statistical properties of an interference pattern, such that any imperfection in the measurement can never overestimate number coherently superposed amplitudes.

We present a universal mechanism that, acting on any target qubit, propagates it to the state had T time units before experiment started. This protocol works by setting superposition of flight paths, where is acted uncharacterized, but repeatable, quantum operations. Independently effect each these individual operations target, successful interference paths causes leap its past state. prove for generic interaction effects, system will reach desired with probability 1 after some finite number steps.