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arXiv:1912.03475 · Physical Review A

Simultaneous multiple-user quantum communication across a spin-chain channel

Rozhin Yousefjani, Abolfazl Bayat

Published Jul 15, 2020• 21 citations
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Abstract

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 sender-receiver pair can share the channel at each time. This significantly limits the rate of communication in a network of many users because 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 crosstalk. The protocol is robust against various imperfections and we specifically show that our protocol can be experimentally realized on currently available superconducting quantum simulators.

DOI
10.1103/physreva.102.012418

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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 sender-receiver pair can share the channel at each time. This significantly limits the rate of communication in a network of many users because 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 crosstalk. The protocol is robust against various imperfections and 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 increases the rate of gate operations without creating crosstalk. This is achieved by tuning the Hamiltonian parameters appropriately, described in the form of two different strategies. The tuning of the parameters makes different bilocalized eigenstates responsible for the realization of the entangling gates between different pairs of distant qubits. Remarkably, the performance of our protocol is robust against increasing the length of the data-bus and the number of users. Moreover, we show that this protocol can tolerate various types of disorders and is applicable in the context of superconductor-based systems. The proposed protocol can serve for realizing two-way quantum communication.
Data multiplexing within a quantum computer can allow for the simultaneous transfer of multiple streams of information over a shared medium thereby minimizing the number of channels needed for requisite data transmission. Here, we investigate a two-way quantum communication protocol using a spin chain placed in an external magnetic field. In our scheme, Alice and Bob each play the role of a sender and a receiver as two states, $\mathrm{cos}(\frac{{\ensuremath{\theta}}_{1}}{2})\left|0\right\ensuremath{\rangle}+\mathrm{sin}(\frac{{\ensuremath{\theta}}_{1}}{2}){e}^{i{\ensuremath{\varphi}}_{1}}\left|1\right\ensuremath{\rangle}$ and $\mathrm{cos}(\frac{{\ensuremath{\theta}}_{2}}{2})\left|0\right\ensuremath{\rangle}+\mathrm{sin}(\frac{{\ensuremath{\theta}}_{2}}{2}){e}^{i{\ensuremath{\varphi}}_{2}}\left|1\right\ensuremath{\rangle}$, are transferred through one channel simultaneously. We find that the transmission fidelity at each end of a spin chain can usually be enhanced by the presence of a second party. This is an important result for establishing the viability of duplex quantum communication through spin chain networks.
Generating high-quality multiparticle entanglement between communicating parties is the primary resource in quantum teleportation protocols. To this aim, we show that the natural dynamics of a single spin chain is able to sustain the generation of two pairs of Bell states----possibly shared between a sender and a distant receiver---which can in turn enable two-qubit teleportation. In particular, we address a spin-12\frac{1}{2}21​ chain with XXXXXX interactions, connecting two pairs of spins located at its boundaries, playing the roles of sender and receiver. In the regime where both end pairs are weakly coupled to the spin chain, it is possible to generate at predefinite times a state that has vanishing infidelity with the product state of two Bell pairs, thereby providing nearly unit fidelity of teleportation. We also derive an effective Hamiltonian via a second-order perturbation approach that faithfully reproduces the dynamics of the full system.
Two different models are presented that allow for efficiently performing routing of a quantum state. Both cases involve an XXXXXX spin chain working as a data bus and additional spins that play the role of sender and receivers, one of which is selected to be the target of the quantum state transmission protocol via a coherent quantum coupling mechanism making use of local and/or global magnetic fields. Quantum routing is achieved in the first of the models considered by weakly coupling the sender and the receiver to the data bus. On the other hand, in the second model, local magnetic fields acting on additional spins located between the sender and receiver and the data bus allow us to perform high-fidelity routing.
Efficient communication between distant qubits is one of the central challenges in scaling quantum processors. Although engineered spin chain protocols have been extensively investigated theoretically, their experimental realization has remained comparatively limited. Here, we experimentally realize engineered quantum communication protocols through digitally simulated spin Hamiltonian on IonQ's Forte 1/ Forte Enterprise 1 trapped-ion quantum processor. Combining exact numerical simulations with quantum hardware experiments, we benchmark uniform nearest-neighbour and engineered coupling profiles and demonstrate that engineered interactions significantly enhance the fidelity of quantum state transfer. We further show that exploiting the commutation structure of the spin Hamiltonian enables a parallel Trotter decomposition that more faithfully reproduces the target dynamics while substantially reducing the circuit depth and execution time compared to the conventional sequential implementations. Our results demonstrate that programmable quantum processors can effectively realize and efficiently implement quantum communication protocols, bringing Hamiltonian-based quantum communication closer to practical quantum technologies.
We present a couple of counterdiabatic (CD) schemes for a rapid and high-fidelity transfer of quantum state across a one-dimensional spin chain, between two weakly coupled external qubits at each end. Employing the effective low-energy Hamiltonian of the system, we first construct the optimal CD terms based on the variational principle and then put forward two experimentally feasible shortcuts, which only need to manipulate couplings between the external qubits and chain. Compared to traditional adiabatic protocol, the resulting schemes allow a drastic increase in state-transfer fidelity in a short time. Furthermore, numerical simulation demonstrates that our speed-up protocols hold robustness against the imperfections of control fields and evolution time. The proposed schemes may be applicable to fast quantum-information transport in various spin-based physical systems.