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We investigate photoinduced proton-coupled electron transfer (PI-PCET)

reaction through a recently devel- oped quasi-diabatic (QD) quantum dynamics

propagation scheme. This scheme enables interfacing accurate diabatic-based

quantum dynamics approaches with adiabatic electronic structure calculations

for on-the-fly simulations. Here, we use the QD scheme to directly propagate

PI-PCET quantum dynamics with the di- abatic Partial Linearized Density Matrix

The goal of entanglement distillation is to turn a large number of weakly

entangled states into a smaller number of highly entangled ones. Practical

entanglement distillation schemes offer a tradeoff between the fidelity to the

target state, and the probability of successful distillation. Exploiting such

tradeoffs is of interest in the design of quantum repeater protocols. Here, we

present a number of methods to assess and optimise entanglement distillation

- Read more about Optimising practical entanglement distillation. (arXiv:1803.10111v1 [quant-ph])
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We investigate the modified trace distance measure of coherence recently

introduced in [Phys. Rev. A 94, 060302(R) (2016)]. We show that for any

single-qubit state, the modified trace norm of coherence is equal to the

$l_{1}$-norm of coherence. For any $d$-dimensional quantum system, an

analytical formula of this measure for a class of maximally coherent mixed

states is provided. The trade-off relation between the coherence quantified by

the new measure and the mixedness quantified by the trace norm is also

We investigate the performance of discrimination strategy in the comparison

task of known quantum states. In the discrimination strategy, one infers

whether or not two quantum systems are in the same state on the basis of the

outcomes of separate discrimination measurements on each system. In some cases

with more than two possible states, the optimal strategy in minimum-error

comparison is that one should infer the two systems are in different states

without any measurement, implying that the discrimination strategy performs

We map the density matrix of the qubit (spin-1/2) state associated with the

Bloch sphere and given in the tomographic probability representation onto

vertices of a triangle determining Triada of Malevich's squares. The three

triangle vertices are located on three sides of another equilateral triangle

with the sides equal to $\sqrt 2$. We demonstrate that the triangle vertices

are in one-to-one correspondence with the points inside the Bloch sphere and

show that the uncertainty relation for the three probabilities of spin

The prospect of computational hardware with quantum advantage relies

critically on the quality of quantum gate operations. Imperfect two-qubit gates

is a major bottleneck for achieving scalable quantum information processors.

Here, we propose a generalizable and extensible scheme for a two-qubit coupler

switch that controls the qubit-qubit coupling by modulating the coupler

frequency. Two-qubit gate operations can be implemented by operating the

coupler in the dispersive regime, which is non-invasive to the qubit states. We

A reliable, triggered photon source is required for many aspects of quantum

technology. Organic molecules are attractive for this application because they

can have high quantum yield and can be photostable, even at room temperature.

For the trigger pulse to generate a photon with high probability, it must

excite the molecule efficiently. We develop a simple model for that efficiency

and discuss how to optimise it. We demonstrate the validity of our model

through experiments on a single dibenzoterrylene (DBT) molecule in an

Quantum violation of Bell inequalities is now used in many quantum

information applications and it is important to analyze it both quantitatively

and conceptually. In the present paper, we analyze violation of multipartite

Bell inequalities via the local probability model - the LqHV (local quasi

hidden variable) model [Loubenets, J. Math. Phys. 53, 022201 (2012)],

incorporating the LHV model only as a particular case and correctly reproducing

the probabilistic description of every quantum correlation scenario, more

By simultaneously coupling multiple two-level artificial atoms to two

superconducting resonators, we design a quantum switch that tunes the

resonator-resonator coupling strength from zero to a large value proportional

to the number of qubits. This process is implemented by engineering the qubits

into different subradiant states, where the microwave photons decay from

different qubits destructively interfere with each other such that the

resonator-resonator coupling strength keeps stable in an open environment.

Strong quantum nonlinearity gives rise to many interesting quantum effects

and has wide applications in quantum physics. Herewe investigate the quantum

nonlinear effect of an optomechanical system (OMS) consisting of both linear

and quadratic coupling. Interestingly, a controllable optomechanical

nonlinearity is obtained by applying a driving laser into the cavity. This

controllable optomechanical nonlinearity can be enhanced into a strong coupling

regime, even if the system is initially in the weak-coupling regime. Moreover,