# All

It is difficult to calculate the energy levels and eigenstates of a large

physical system on a classical computer because of the exponentially growing

size of the Hilbert space. In this work, we experimentally demonstrate a

quantum algorithm which could solve this problem via simulated resonant

transitions. Using a four-qubit quantum simulator in which two qubits are used

as ancillas for control and measurement, we obtain the energy spectrum of a

2-qubit low-energy effective Hamiltonian of the water molecule. The simulated

We establish a connection between non-Markovianity and negative entropy

production rate for various classes of quantum operations. Generalizing the

definition of the entropy production rate for the non-equilibrium case we

connect it with the rate of change of free energy of the system, and establish

complementary relations between non-Markovianity and maximum loss of free

energy. We naturally conclude that non-Markovianity in terms of divisibility

breaking is a necessary resource for the backflow of other resources like

By introducing finite next-nearest-neighboring (NNN) intersite coupling, we

investigate the eigenenergies of the $\cal PT$-symmetric non-Hermitian

Su-Schrieffer-Heeger (SSH) model with two conjugated imaginary potentials at

the end sites. It is found that the NNN intersite coupling plays a special role

in modifying the eigenenergy spectra of both the bulk states and the

topological end states. Due to the strengthening of NNN coupling, the bonding

band is first narrowed and then undergoes the top-bottom reversal followed by

We have investigated how memory effects on the teleportation of quantum

Fisher information(QFI) for a single qubit system using a class of X-states as

resources influenced by decoherence channels with memory, including amplitude

damping, phase-damping and depolarizing channels. Resort to the definition of

QFI, we first derive the explicit analytical results of teleportation of QFI

with respect to weight parameter $\theta$ and phase parameter $\phi$ under the

In this paper, we consider the feedback stabilization problem for N-level

quantum angular momentum systems undergoing continuous-time measurements. By

using stochastic and geometric control tools, we provide sufficient conditions

on the feedback control law ensuring almost sure exponential convergence to a

predetermined eigenstate of the measurement operator. In order to achieve these

results, we establish general features of quantum trajectories which are of

A recent paper [arXiv:1901.05477v1] claims that the CSL model of spontaneous

wave function collapse is ruled out by observations on heat flow from neutron

stars. This type of system-a degenerate Fermi gas-is relevant as it represents

the densest form of matter, potentially maximizing CSL effects. As it turns

out, this is not the case: to leading order, the CSL induced heating is the

same as for ordinary matter, and neutron stars do not bound the CSL parameters

significantly.

Quantum correlations in an entangled many-body system are capable of storing

information. Even when the information is injected by a local unitary operation

to the system, the entanglement delocalizes it. In a recent study on

multiple-qubit systems, it is shown that a virtual qubit defined in the

correlation space plays a role of perfect storage of delocalized information,

which is calld a quantum information capsule (QIC). In this paper, we extend

the analysis to multiple-qudit systems and construct a QIC for general write

A theoretical parallel between the classical Brownian motion and quantum

mechanics is explored. It is shown that, in contrast to the classical Langevin

force, quantum mechanics is driven by turbulent velocity fluctuations with

diffusive behavior. In the case of simultaneous action of the two stochastic

sources, the quantum Brownian motion takes place, which is theoretically

described as well.

In this work, we demonstrate initialization and readout of nuclear spins via

a negatively charged silicon-vacancy (SiV) electron spin qubit. Under

Hartmann-Hahn conditions the electron spin polarization is coherently

transferred to the nuclear spin. The readout of the nuclear polarization is

observed via the fluorescence of the SiV. We also show that the coherence time

of the nuclear spin (6 ms) is limited by the electron spin-lattice relaxation

due to the hyperfine coupling to the electron spin. This work paves the way

Two-dimensional Nuclear Magnetic Resonance (NMR) is essential to molecule

structure determination. Nitrogen vacancy (NV) center in diamond has been

proposed and developed as an outstanding quantum sensor to realize NMR in

nanoscale. However, it is still lack of two-dimensional nanoscale NMR

spectroscopy which is crucial in structure analysis. In our work, combined

two-dimensional quantum controls with an artificial intelligence algorithm, the

two-dimensional nanoscale NMR spectroscopy is realized on a pair of coupled 13C