The manipulation of multiple qubits, all in superposition and entangled, is the one-two punch powering computation and sensing in sought-after quantum-based technologies. “Without superposition and lots of entanglement, you can’t build a quantum computer,” said Safavi-Naeini.

To demonstrate these quantum effects in the experiment, the Stanford researchers generated a single qubit, stored as a photon in the circuit on the bottom chip. The circuit was then allowed to exchange energy with one of the mechanical oscillators on the top chip before transferring the remaining information to the second mechanical device. By exchanging energy in this way – first with one mechanical oscillator, and then with the second oscillator – the researchers used the circuit as a tool to quantum mechanically entangle the two mechanical resonators with each other.

“The bizarreness of quantum mechanics is on full display here,” said Wollack. “Not only does sound come in discrete units, but a single particle of sound can be shared between the two entangled macroscopic objects, each with trillions of atoms moving – or not moving – in concert.”

For eventually performing practical calculations, the period of sustained entanglement, or coherence, would need to be significantly longer – on the order of seconds instead of the fractions of seconds achieved so far. Superposition and entanglement are both highly delicate conditions, vulnerable to even slight disturbances in the form of heat or other energy, and accordingly endow proposed quantum sensing devices with exquisite sensitivity. But Safavi-Naeini and his co-authors believe longer coherence times can be readily achievable by honing the fabrication processes and optimizing the materials involved.

“We’ve improved the performance of our system over the last four years by nearly 10 times every year,” said Safavi-Naeini. “Moving forward, we will continue to make concrete steps toward devising quantum mechanical devices, like computers and sensors, and bring the benefits of mechanical systems into the quantum domain.”

Additional co-authors on the paper include Rachel G. Gruenke, Zhaoyou Wang, and Patricio Arrangoiz-Arriola of the Department of Applied Physics in Stanford’s School of Humanities and Sciences.

The research was funded by the David and Lucile Packard, Stanford Graduate, and Sloan Fellowships. This work was funded by Amazon Inc., U.S. Office of Naval Research, U.S. Department of Energy, National Science Foundation, Army Research Office, and NTT Research.

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