We develop an abstract way of defining linear-optics networks designed to perform quantum information tasks such as quantum gates. We will be mainly concerned with the nonlinear sign shift gate, but it will become obvious that all other gates can be treated in a similar manner. The abstract scheme is extremely well suited for analytical as well as numerical investigations since it reduces the number of parameters for a general setting. With that we show numerically and partially analytically for a wide class of states that the success probability of generating a nonlinear sign shift gate does not exceed 1/4 which to our knowledge is the strongest bound to date.
Universal quantum gates lie at the heart of designing quantum computer. We construct two compact quantum circuits to implement post-selected controlled-phase-flip (CPF) gate and Toffoli gate with linear optics assisted by one and two single photons, respectively. The current existing maximum success probability of 1/4 for linear optical CPF gate is achieved by resorting to an ancillary single photon rather than an entangled photon pair or two single photons. Remarkably, our Toffoli gate is accomplished with current maximum success probability of 1/30 without using additional entangled photon p…
We proposed two entanglement concentration protocols (ECPs) to obtain maximally entangled Greenberger-Horne-Zeilinger (GHZ)-type entangled coherent state (ECS) from the corresponding partially entangled GHZ-type ECSs. We obtained the first ECP using a partially entangled GHZ-type ECS assisted with a superposition of single-mode coherent state, however the second ECP is designed using two copies of partially entangled GHZ-type ECSs. The success probabilities have also been calculated and discussed for both the ECPs. We have further compared the success probabilities of our first ECP for 3-mode …
Quantum annealing aims at finding optimal solutions to complex optimization problems using a suitable quantum many body Hamiltonian encoding the solution in its ground state. To find the solution one typically evolves the ground state of a soluble initial Hamiltonian adiabatically to the ground state of the designated final Hamiltonian. Here we explore whether and when a full quantum representation of the dynamics leads to higher probability to end up in the desired ground when compared to a classical mean field approximation. As simple, nontrivial example we target the ground state of interac…
We present a novel semi-analytical methodology to construct optimal linear optical circuits for heralded production of 3-photon GHZ and 2-photon Bell states. We provide a detailed description and analysis of the resulting optical schemes, which deliver success probabilities of 1/54 and 2/27 for dual-rail encoded 3-GHZ and Bell states generation, respectively. Our results improve the known constructive bounds on the success probabilities for 3-GHZ states and are of particular importance for a ballistic quantum computing model, for which these states provide an essential resource.
We explore the multiparticle transition probabilities in Gaussian unitaries effected by a two-mode Bogoliubov bosonic transformation on the mode annihilation and creation operators. We show that the transition probabilities can be characterized by remarkably simple, yet unsuspected recurrence equations involving a linear combination of probabilities. The recurrence exhibits an interferometric suppression term - a negative probability - which generalizes the seminal Hong-Ou-Mandel effect to more than two indistinguishable photons impinging on a beam splitter of rational transmittance. Unexpecte…
Subjectivists about Quantum Probabilities Should be Realists about Quantum States
有大量的文献，其中包括伊塔马尔·皮托夫斯基（Itamar Pitowksy）的《对测量结果的打赌》（Betting on Outcomes of Measurements），它揭示了量子力学的结构，以及量子力学与经典力学的不同之处，即通过将理论置于实验结果上的代理人的赌注中。虽然这种方法本身对于量子可观测量和量子态的本体论地位是中立的，但有些人，特别是那些采用“QBism”标签作为他们观点的人，认为这种方法提供了得出结论的动机，即量子态在物理现实中不代表任何东西，而是仅仅编码了代理人的信念。在本章中，我将论证，如果结论是关于行为者的信念的，那么当所涉及的概率被认为是主观的时，关于量子态的实在论的论证就通过了：一个信念符合量子概率的行为者应该相信，她与不同的纯量子态相关联的准备过程产生了不同的实在态。这个结论只能通过对行动者关于世界的理论化的限制的规定来避免，这些限制是量子力学的经验成功或任何其他经验考虑所不能保证的。量子概率的主观主义者应该是量子态的实在主义者。
Violations of Bell inequalities in classical optics have been demonstrated in terms of field mean intensities and correlations, however, the quantum meaning of violations point to statistics and probabilities. We present a violation of Bell inequalities for classical fields in terms of probabilities, where we convert classical-field intensities into probabilities via the standard photon-counting equation. We find violation for both, entangled and separable field states. We conclude that any obtained quantum effect might be fully ascribed to the quantum nature of the detector rather than the fi…
Non-coherent evolution of closed weakly interacting system leads to equidistribution of probabilities of microstates
Departamento de Fisica de Materia Condensada, GIYA, CAC-CNEA（凝聚态物理系，GIYA，CAC-CNEA）；Instituto de Nanociencia y Nanotecnologia, INN-CONICET-CNEA（纳米科学与技术研究所，INN-CONICET-CNEA）
