Inspired by the functioning of pulsed lasers, scientists from France and Japan have developed an acoustic counterpart that permits the exact and managed transmission of single electrons between quantum nodes.

Riding the waves

The spin of an electron can function a foundation for creating qubits—the fundamental unit of knowledge of quantum computing. In order to course of or retailer that info, the knowledge in qubits might must be transported between quantum nodes in a community.

One possibility is transporting the electrons themselves, one thing that may now be performed by having them experience sound waves. “More than 10 years ago, we demonstrated it for the first time,” mentioned lead researcher Christopher Bauerle of the Grenoble-based Institute Néel.

However, this method had a big disadvantage. Like any wave, a sound wave takes a sinusoidal kind, consisting of many maxima and minima, which makes it tough to foretell the situation of the electron.

Bauerle and his staff have now gotten round this downside by engineering a wave that has a single minimal or a single most. “By using a technique called Fourier synthesis, we superposed many waves with different frequencies in such a way that there was only one minimum or one maximum depending on whether you apply positive or negative voltage,” he mentioned.

Bauerle compares these concentrated sound waves to laser pulses. “If you want to perform time-resolved measurements, you excite a system with a short laser pulse. We use a similar technique in our system using sound. Since we have a focused acoustic pulse, we know exactly at what time the electron will arrive at a node,” he mentioned.

Paulo Santos, a Berlin-based nanoelectronics professional from the Paul Drude Institute for Solid State Electronics, likens the method to a surfer using a wave. “Just like a surfer will get transported by a wave in an ocean, the electron qubit rides the floor acoustic wave to maneuver within the quantum community,” Santos, who was not a part of the research, remarked.

Making waves

To generate these sound waves, a chip containing quantum nodes was embedded in a gallium-arsenide crystal linked to 2 gold-plated electrodes deposited onto a piezoelectric substrate. An electrical subject is generated by making use of an alternating voltage to those electrodes. The various electrical subject deforms the piezoelectric materials and generates floor acoustic waves. They are accompanied by a transferring electrical subject (generated by the inverse piezoelectric impact) that helps to move the electrons.

Bauerle listed a number of benefits of this technique, which works at temperatures between 20 milliKelvin to at least one Kelvin. “The electrons get transported between the nodes on the velocity of sound (3,000 m/s). This, together with the exact and managed method of electron transmission, allows us to control the quantum info in actual time. If you examine it to the photonic quantum system, the manipulations must be performed beforehand as a result of info is transmitted on the velocity of sunshine, which is just too quick for real-time manipulation,” he mentioned.

Moreover, this method can probably be scaled up due to the big dimension of the waveform. “A single acoustic wave can carry electrons from completely different quantum nodes on the identical time,” Bauerle mentioned, including that they achieved 99.4 p.c transmission effectivity throughout their experiments.

According to Santos, this method’s distinctive means to exactly transport qubits in addition to manipulate them on the fly on a chip might have numerous distinct purposes sooner or later. “The subsequent massive step is demonstrating the entanglement of those flying qubits. The different massive effort goes to be to switch this know-how from gallium arsenide to different supplies like silicon.”

He added, nevertheless, that it might take years earlier than seeing sensible purposes based mostly on this analysis.

Santos highlighted that electron spins are simply considered one of many approaches for processing quantum info; different choices embrace photons, superconducting qubits, and chilly atoms. He identified that photon qubits will stay a mainstream method in quantum methods.

“There are extra individuals engaged on photon-based quantum processing as a result of there already exists an enormous infrastructure. For instance, silicon-based chips even have built-in optics. The ‘electron surfing’ method is suitable with on-chip integration and may revenue from these developments,” he mentioned, suggesting that advances in a single may also help with the opposite.

Physical Review X, 2022. DOI: 10.1103/PhysRevX.12.031035

Dhananjay Khadilkar is a journalist based mostly in Paris.