Detection of Atomic Vibrations Paves Way for Quantum Tech Advancements

A team of scientists at the University of Washington has discovered the phenomena of atomic vibrations, referred to as “breathing.” This observation could assist in encoding and transferring quantum information. Additionally, they have developed a new device that can interact with these atomic vibrations and light emissions, thereby propelling the progress of quantum technology.

By utilizing a laser to excite the atoms, the researchers have been able to detect atomic breathing, which is the mechanical movement between two atomic layers. The sound produced by this process may potentially aid in the encoding and transmission of quantum data.

Along with this, the researchers have also created a device that could provide a fresh building block for quantum technologies. These technologies are expected to find widespread application in areas like computing, communication, and sensor development in the future.

The findings of the research team have been recently published in the journal Nature Nanotechnology.

“With this new atomic-scale platform, we’re utilizing what’s known in the scientific community as ‘optomechanics,’ where light and mechanical motions are intimately linked,” said Mo Li, the senior author of the study, who is a professor of both electrical and computer engineering and physics at the University of Washington. “This gives rise to a unique quantum effect that can be harnessed to control single photons navigating through integrated optical circuits for a variety of applications.”

Adina Ripin. Credit: University of Washington

In prior research, the team had focused on a quantum-level quasiparticle called an “exciton.” It is possible to encode information into an exciton which can then be emitted as a photon – the fundamental quantum unit of light. Each photon carries quantum properties like polarization, wavelength, and emission timing, which can serve as a quantum bit, or “qubit,” vital for quantum computing and communication. Since this qubit is transported by a photon, it moves at the speed of light.

“To feasibly build a quantum network, we need reliable methods for creating, manipulating, storing, and transmitting qubits,” stated lead author Adina Ripin, a doctoral physics student at the University of Washington. “Given the efficiency of optical fibers in transporting photons over long distances at high speeds, with minimal energy or information loss, photons are a natural choice for this quantum information transmission.”

The team worked with excitons to create a single photon emitter or “quantum emitter,” an essential component for light and optics-based quantum technologies. To achieve this, they layered tungsten and selenium atoms, creating tungsten diselenide, atop one another.

Mo Li. Credit: University of Washington

When the researchers applied a specific pulse of laser light, they dislodged an electron from a tungsten diselenide atom’s nucleus, generating an exciton quasiparticle. Each exciton was comprised of a negatively charged electron on one tungsten diselenide layer and a positively charged vacancy, or “hole,” on the other, where the electron used to reside. Opposite charges attracted each other, causing the electron and the hole to bond tightly. Shortly after, as the electron returned to its previous position, the exciton emitted a photon encoded with quantum information, thereby producing the desired quantum emitter.

The team also discovered that the tungsten diselenide atoms were emitting another type of quasiparticle, a phonon. Phonons, caused by atomic vibrations akin to breathing, were produced as the two atomic layers of the tungsten diselenide vibrated like tiny drumheads. This is the first instance of phonons being observed in a single photon emitter within such a two-dimensional atomic system.

The research team noted equally spaced peaks when measuring the spectrum of the emitted light. Each photon released by an exciton was coupled with one or more phonons, visually represented by the equally spaced peaks on the energy spectrum.

“Phonon is the inherent quantum vibration of the tungsten diselenide material, and it stretches the exciton electron-hole pair vertically across the two layers,” explained Li. “This has a dramatic impact on the optical properties of the photon emitted by the exciton, a phenomenon never reported before.”

The researchers investigated the potential of exploiting phonons for quantum technology. By applying electrical voltage, they observed changes in the interaction energy between the phonons and the emitted photons. This variation was controllable and measurable, pertinent to encoding quantum information into a single photon emission, and was achieved in one integrated system.

The team plans to scale up the system and build a waveguide – fibers on a chip that capture single photon emissions and guide them to their destination. They aim to control multiple emitters and their associated phonon states, rather than one at a time. This will enable the quantum emitters to communicate, contributing to the establishment of quantum circuitry.

“Our ultimate goal is to develop an integrated system with quantum emitters capable of utilizing single photons running through optical circuits and the newly discovered phonons for quantum computing and sensing,” Li said. “This breakthrough will significantly aid our efforts and foster the development of quantum computing, which is projected to have numerous applications in the future.”

The study, titled “Tunable phononic coupling in excitonic quantum emitters,” was authored by Adina Ripin, Ruoming Peng, Xiaowei Zhang, Srivatsa Chakravarthi, Minhao He, Xiaodong Xu, Kai-Mei Fu, Ting Cao, and Mo Li, and was published on 1 June 2023 in Nature Nanotechnology.

Additional co-authors of the study are Ruoming Peng, Xiaowei Zhang, Srivatsa Chakravarthi, Minhao He, Xiaodong Xu, Kai-Mei Fu, and Ting Cao.

The National Science Foundation provided funding for the study.

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