Abstract
Surface acoustic waves are commonly used in classical electronics applications, and their use in quantum systems is beginning to be explored, as evidenced by recent experiments using acoustic Fabry–Pérot resonators. Here we explore their use for quantum communication, where we demonstrate a single-phonon surface acoustic wave transmission line, which links two physically separated qubit nodes. Each node comprises a microwave phonon transducer, an externally controlled superconducting variable coupler, and a superconducting qubit. Using this system, precisely shaped individual itinerant phonons are used to coherently transfer quantum information between the two physically distinct quantum nodes, enabling the high-fidelity node-to-node transfer of quantum states as well as the generation of a two-node Bell state. We further explore the dispersive interactions between an itinerant phonon emitted from one node and interacting with the superconducting qubit in the remote node. The observed interactions between the phonon and the remote qubit promise future quantum-optics-style experiments with itinerant phonons.
Highlights
Quantum communication is of significant interest for the generation of remote entanglement and the secure transmission of information, as well as for distributed quantum computing[1,2,3,4,5,6,7]
For frequencies inside the transducer’s active band, from 3.87 to 4.01 GHz, where the emission is almost entirely unidirectional itinerant phonons, we observe a timedelayed revival of qubit Q1’s excited state population PQe 1 at times that are multiples of the phonon round-trip time τRT ~ 1 μs, each revival corresponding to the traveling phonon reflecting off the other transducer before re-exciting Q1
In conclusion, we demonstrate controlled phonon-mediated quantum state transfer and remote entanglement between two quantum nodes, each node comprising a superconducting qubit with a time-variable coupler, using individual itinerant SAW phonons traveling in an acoustic transmission line after a controlled, on-demand release, followed by capture
Summary
Quantum communication is of significant interest for the generation of remote entanglement and the secure transmission of information, as well as for distributed quantum computing[1,2,3,4,5,6,7].There are several demonstrations of long-distance quantum communication protocols using optical methods, in parallel with demonstrations of similar protocols using microwave-frequency photons, including Bell state entanglement of remote qubits as well as the transmission of multi-qubit entangled states[8,9,10,11,12,13,14,15,16].Microwave-frequency phonons, as opposed to photons, can be used for quantum communication as well as for coupling hybrid quantum systems[17,18,19,20], in the latter case taking advantage of the strong strain coupling in some optical as well as atomicscale systems. Quantum communication is of significant interest for the generation of remote entanglement and the secure transmission of information, as well as for distributed quantum computing[1,2,3,4,5,6,7]. There are several demonstrations of long-distance quantum communication protocols using optical methods, in parallel with demonstrations of similar protocols using microwave-frequency photons, including Bell state entanglement of remote qubits as well as the transmission of multi-qubit entangled states[8,9,10,11,12,13,14,15,16]. Recent advances in the quantum control of phonons include the creation and measurement of stationary phonon quantum states[22,23,24], the emission and absorption of phonons in an acoustic resonator[25], and the generation of entangled phonons in a phonon-mediated quantum eraser experiment[26]
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