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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