Although it may seem The Delayed Choice experiments contradict causality and

one could construct an experiment which could possibly affect the past, using

Many World interpretation we prove it is not possible. We also find a

mathematical background to Which-path information and show why its

obtainability prevents system from interfering. We find a system which exhibit

both interference and correlation and show why one-particle interference and

correlations are complementary. Better visible interference pattern leads to

# All

An initial coherent state is propagated exactly by a kicked quantum

Hamiltonian and its associated classical stroboscopic map. The classical

trajectories within the initial state are regular for low kicking strengths,

then bifurcate and become mainly chaotic as the kicking parameter is increased.

Time-evolution is tracked using classical, quantum and semiclassical Wigner

functions, obtained via the Herman-Kluk propagator. Quantitative comparisons

are also included and carried out from probability marginals and

There is a remarkable characteristic of photosynthesis in nature, that is,

the energy transfer efficiency is close to 100%. Recently, due to the rapid

progress made in the experimental techniques, quantum coherent effects have

been experimentally demonstrated. Traditionally, the incoherent theories are

capable of calculating the energy transfer efficiency, e.g., (generalized)

F\"orster theory and modified Redfield theory. However, in order to describe

Quantum simulation of chemical systems is one of the most promising near-term

applications of quantum computers. The variational quantum eigensolver, a

leading algorithm for molecular simulations on quantum hardware, has a serious

limitation in that it typically relies on a pre-selected wavefunction ansatz

that results in approximate wavefunctions and energies. Here we present an

arbitrarily accurate variational algorithm that instead of fixing an ansatz

Implementing high-fidelity two-qubit gates in single-electron spin qubits in

silicon double quantum dots is still a major challenge. In this work, we employ

analytical methods to design control pulses that generate high-fidelity

entangling gates for quantum computers based on this platform. Using realistic

parameters and initially assuming a noise-free environment, we present simple

control pulses that generate CNOT, CPHASE, and CZ gates with average fidelities

We theoretically study the quantum interference induced photon blockade

phenomenon in atom cavity QED system, where the destructive interference

between two different transition pathways prohibits the two-photon excitation.

Here, we first explore the single atom cavity QED system via an atom or cavity

drive. We show that the cavity-driven case will lead to the quantum

interference induced photon blockade under a specific condition, but the atom

driven case can't result in such interference induced photon blockade. Then, we

This paper develops the resource theory of asymmetric distinguishability for

quantum channels, generalizing the related resource theory for states

[arXiv:1006.0302, arXiv:1905.11629]. The key constituents of the channel

resource theory are quantum channel boxes, consisting of a pair of quantum

channels, which can be manipulated for free by means of an arbitrary quantum

superchannel (the most general physical transformation of a quantum channel).

Quantum vision is currently emerging as an interdisciplinary field

synthesizing the physiology of human vision with modern quantum optics. We

recently proposed a biometric scheme based on the human visual system's ability

to perform photon counting. We here present a light stimulus source that can

provide for the requirements of this biometric scheme, namely a laser light

beam having a cross section consisting of discrete pixels, allowing for an

arbitrary pattern of illuminated pixels, each having a photon number per unit

We prove that the classical capacity of an arbitrary quantum channel assisted

by a free classical feedback channel is bounded from above by the maximum

average output entropy of the quantum channel. As a consequence of this bound,

we conclude that a classical feedback channel does not improve the classical

capacity of a quantum erasure channel, and by taking into account energy

constraints, we conclude the same for a pure-loss bosonic channel. The method

for establishing the aforementioned entropy bound involves identifying an

We propose a brand-new protocol called machine learning continuous-variable

quantum key distribution (ML-CVQKD), aiming to break the limitation of

traditional pattern in CVQKD and establish a cross research platform between

CVQKD and machine learning. ML-CVQKD divides the whole system into state

learning process and state prediction process. The former is used for training

and estimating quantum classifier, and the latter is used for predicting

unlabeled signal states. Meanwhile, a quantum multi-label classification (QMLC)