The time evolution of spin chains has been extensively studied for transferring quantum states between different registers of a quantum computer. Nonetheless, in most of these protocols only one pair of sender-receivers can share the channel at each time. This significantly limits the rate of communication in a network of many users as they can only communicate through their common data-bus sequentially and not all at the same time. Here, we propose a protocol in which multiple users can share a spin chain channel simultaneously without having crosstalk between different parties. This is achieved by properly tuning the local parameters of the Hamiltonian to mediate an effective interaction between each pair of users via a distinct set of energy eigenstates of the system. We introduce three strategies with different levels of Hamiltonian tuning, each might be suitable for a different physical platform. All the three strategies provide very high transmission fidelities with vanishingly small crosstalks. We specifically show that our protocol can be experimentally realized on currently available superconducting quantum simulators.
The power of a quantum circuit is determined through the number of two-qubit entangling gates that can be performed within the coherence time of the system. In the absence of parallel quantum gate operations, this would make the quantum simulators limited to shallow circuits. Here, we propose a protocol to parallelize the implementation of two-qubit entangling gates between multiple users which are spatially separated, and use a commonly shared spin chain data-bus. Our protocol works through inducing effective interaction between each pair of qubits without disturbing the others, therefore, it…
Quantum communication enables a host of applications that cannot be achieved by classical communication means, with provably secure communication as one of the prime examples. The distance that quantum communication schemes can cover via direct communication is fundamentally limited by losses on the communication channel. By means of quantum repeaters, the reach of these schemes can be extended and chains of quantum repeaters could in principle cover arbitrarily long distances. In this work, we provide two efficient algorithms for determining the generation time and fidelity of the first gener…
Composable simultaneous purification: when all communication scenarios reduce to spatial correlations
Sorbonne Université（索邦大学）；CNRS（法国国家科学研究中心）；LIP6（LIP6实验室）；School of Informatics, University of Edinburgh（爱丁堡大学信息学院）；Université Grenoble Alpes（格勒诺布尔阿尔卑斯大学）；Grenoble INP（格勒诺布尔理工学院）；LIG（LIG实验室）
The communication cost of a classical protocol is typically measured in terms of the number of bits communicated for this determines the time required for communication during the protocol. Similarly, for quantum communication protocols, which use finite-dimensional quantum states, the communication cost is measured in terms of the number of qubits communicated. However, in quantum physics, one can also use infinite-dimensional states, like optical quantum states, for communication protocols. Communication cost measures based on counting the (equivalent) number of qubits transmitted during com…
Enhancing fidelity in teleportation of a two-qubit state via a quantum communication channel formed by spin-1/2 Ising-Heisenberg trimer chains due to a magnetic field
We consider several models of 1-round classical and quantum communication, some of these models have not been defined before. We "almost separate" the models of simultaneous quantum message passing with shared entanglement and the model of simultaneous quantum message passing with shared randomness. We define a relation which can be efficiently exactly solved in the first model but cannot be solved efficiently, either exactly or in 0-error setup in the second model. In fact, our relation is exactly solvable even in a more restricted model of simultaneous classical message passing with shared e…
A relational bipartite communication problem is presented that has an efficient quantum simultaneous-messages protocol, but no efficient classical two-way protocol.
Software-enhanced simultaneous quantum-classical communication protocol with Gaussian post-selection
University of Queensland（昆士兰大学）；A*STAR Quantum Innovation Centre (Q.InC), Agency for Science, Technology and Research (A*STAR)（A*STAR量子创新中心（Q.InC），科学技术研究局（A*STAR））
Quantum communication enables the implementation of tasks that are unachievable with classical resources. However, losses on the communication channel preclude the direct long-distance transmission of quantum information in many relevant scenarios. In principle quantum repeaters allow one to overcome losses. However, realistic hardware parameters make long-distance quantum communication a challenge in practice. For instance, in many protocols an entangled pair is generated that needs to wait in quantum memory until the generation of an additional pair. During this waiting time the first pair d…
In 1999 Raz demonstrated a partial function that had an efficient quantum two-way communication protocol but no efficient classical two-way protocol and asked, whether there existed a function with an efficient quantum one-way protocol, but still no efficient classical two-way protocol. In 2010 Klartag and Regev demonstrated such a function and asked, whether there existed a function with an efficient quantum simultaneous-messages protocol, but still no efficient classical two-way protocol. In this work we answer the latter question affirmatively and present a partial function Shape, which can…
Communication Complexity of Private Simultaneous Quantum Messages Protocols
Graduate School of Engineering, Mie University（三重大学大学院工学研究科）；Graduate School of Informatics/Institute for Advanced Study, Nagoya University（名古屋大学情报学研究科／高等研究院）
New Results in the Simultaneous Message Passing Model
考虑以下用于计算X X Y X Z的子集的关系f的同时消息传递（SMP）模型。在这个模型中，Alice在X中的输入x上，Bob在Y中的输入y上，向第三方Reynolds发送一条消息，然后Reynolds输出Z中的z，使得f中的（x，y，z）。我们首先显示最佳的“直和”的结果，在这个模型中的所有关系f，无论是在量子和经典的设置，在这种情况下，我们允许共享资源（共享纠缠在量子协议和公共硬币在经典协议）之间的爱丽丝和Reynolds和鲍勃和Reynolds和没有共享资源之间的爱丽丝和鲍勃。这意味着，在这个模型中，计算f的k个同时实例所需的通信，总体上是恒定成功的，至少是计算一个实例所需的通信的k倍。这特别暗示了Chakrabarti，Shi，Wirth和Yao在2001年针对等式函数（以及一类其他所谓的鲁棒函数）给出的早期直和结果，在任何方之间没有共享资源的经典SMP模型中。此外，我们调查之间的差距smp模型和单向模型的通信复杂性，并展示了一个部分函数，是指数更昂贵的，在前者，如果量子通信纠缠是允许的，相比后者，即使在确定性的情况下。
