Researchers from the University of Washington have discovered that by observing the kind of light those atoms release when triggered by a laser, they may detect atomic “breathing,” or the mechanical oscillation between two layers of atoms. Researchers may be able to encode and communicate quantum information using the sound of this atomic “breath.”
Additionally, the researchers created a tool that might act as a novel form of building block for quantum technologies, which are expected to have a wide range of future applications in industries including computers, communications, and sensor development.
The researchers published these findings on June 1, 2023, in Nature Nanotechnology.
“This is a new, atomic-scale platform, using what the scientific community calls ‘optomechanics,’ in which light and mechanical motions are intrinsically coupled together,” said senior author Mo Li, a UW professor of both electrical and computer engineering and physics. “It provides a new type of involved quantum effect that can be utilized to control single photons running through integrated optical circuits for many applications.”
The group had previously investigated a quantum-level quasiparticle known as a “exciton.” A photon, a minute energy particle regarded as the quantum unit of light, can be used to encode information into an exciton and subsequently release it.
Each photon’s quantum characteristics, including its polarization, wavelength, and/or timing of emission, can serve as a quantum bit of data, or “qubit,” for quantum computing and communication. And because this qubit is carried by a photon, it travels at the speed of light.
“The bird’s-eye view of this research is that to feasibly have a quantum network, we need to have ways of reliably creating, operating on, storing and transmitting qubits,” said lead author Adina Ripin, a UW doctoral student of physics. “Photons are a natural choice for transmitting this quantum information because optical fibers enable us to transport photons long distances at high speeds, with low losses of energy or information.”
A phonon is the natural quantum vibration of the tungsten diselenide material, and it has the effect of vertically stretching the exciton electron-hole pair sitting in the two layers. This has a remarkably strong effect on the optical properties of the photon emitted by the exciton that has never been reported before.
Professor Mo Li
A single photon emitter, or “quantum emitter,” is a crucial part of quantum technologies based on light and optics, and the researchers were working with excitons to generate one. The scientists accomplished this by stacking two thin layers of tungsten diselenide, a material composed of tungsten and selenium atoms.
An exciton quasiparticle was created when the researchers used a precise laser pulse to push an electron away from the nucleus of a tungsten diselenide atom. On one layer of the tungsten diselenide, there was a negatively charged electron, and on the other layer, there was a positively charged hole in the location of the electron.
Additionally, the electron and the hole in each exciton were strongly bound to one another because to the attraction of opposite charges. The exciton then released a single photon carrying quantum information, creating the quantum emitter the researchers was aiming for as the electron quickly fell back into the hole it had previously occupied.
However, the scientists found that the tungsten diselenide atoms were also emitting phonons, a different class of quasiparticle. Atomic vibration, which is analogous to breathing, produces phonons. In this case, the tungsten diselenide’s two atomic layers vibrating in relation to one another like small drumheads produced phonons. This is the first instance of phonons being seen in a single photon emitter in a two-dimensional atomic system of this kind.
The scientists found several evenly spaced peaks in the radiated light’s spectrum when they measured it. Each and every photon that an exciton released was connected to one or more phonons. Similar to stepping up a quantum energy ladder one rung at a time, these energy spikes were visually depicted on the spectrum by the evenly spaced peaks.
“A phonon is the natural quantum vibration of the tungsten diselenide material, and it has the effect of vertically stretching the exciton electron-hole pair sitting in the two layers,” said Li, who is also is a member of the steering committee for the UW’s QuantumX, and is a faculty member of the Institute for Nano-Engineered Systems. “This has a remarkably strong effect on the optical properties of the photon emitted by the exciton that has never been reported before.”
The researchers were curious if they could harness the phonons for quantum technology. They changed the electrical voltage and discovered that they could change the interaction energy of the phonons and photons that were released.
In ways that were pertinent to encoding quantum information into a single photon emission, these variances were quantifiable and controllable. And all of this was completed in a single, integrated system using a relatively small number of atoms.
The scientists will then scale up the technology after creating waveguide fibers on a chip that capture single photon emissions and steer them in the right direction. The team intends to be able to manage numerous emitters and their associated phonon states rather of just one quantum emitter at a time. As a result, the quantum emitters will be able to “talk” to one another, laying the groundwork for quantum circuits.
“Our overarching goal is to create an integrated system with quantum emitters that can use single photons running through optical circuits and the newly discovered phonons to do quantum computing and quantum sensing,” Li said. “This advance certainly will contribute to that effort, and it helps to further develop quantum computing which, in the future, will have many applications.”
