Identifying quantum defects that create photons at specific wavelengths has been challenging. However, funding from the US Department of Energy and the National Science Foundation (NSF) has enabled researchers at the UC Santa Barbara College of Engineering to uncover the reasons. Their findings have been reported in the journal APL Photonics.
Concept illustration depicting a quantum defect emitting a single photon. Image Credit: Mark Turianksy
Computers derive substantial benefits from being connected to the internet, raising the question: How valuable is a quantum computer without a quantum internet?
The key to our current internet's success is its ability to preserve data integrity over long distances, largely achieved through the use of photons—fundamental units of light. Photons are uniquely suited for this task because they interact very weakly with their surroundings, which helps maintain their delicate quantum state over long distances. This property is crucial for carrying quantum information, which relies on preserving entanglement for extended periods. Photons can be produced through various methods, including exploiting atomic-scale imperfections, or quantum defects, in crystals to generate single photons in a specific quantum state.
While fiber-optic cables have been optimized over decades to transmit photons with minimal loss, this efficiency is limited to a narrow wavelength range known as the "telecom wavelength band." Finding quantum defects that emit photons at these wavelengths has been a challenge.
However, with support from the U.S. Department of Energy and the National Science Foundation (NSF), researchers at UC Santa Barbara's College of Engineering have made significant progress in understanding this issue. Their research explores why this difficulty arises and provides insights into designing better quantum emitters.
Atoms are constantly vibrating, and those vibrations can drain energy from a light emitter. As a result, rather than emitting a photon, a defect might instead cause the atoms to vibrate, reducing the light-emission efficiency.
Chris G. Van de Walle, Herbert Kroemer Professor, Materials Science, University of California, Santa Barbara
Van de Walle’s group developed theoretical models to capture the role of atomic vibrations in the photon-emission process and studied how various defect properties influence emission efficiency.
Their research highlights the reasons behind why the efficiency of single-photon emission significantly drops as the emission wavelength moves from the visible range (violet to red) into the infrared spectrum of the telecom band. Additionally, their model provides insights into methods for designing emitters that are both brighter and more efficient.
Choosing the host material carefully, and conducting atomic-level engineering of the vibrational properties are two promising ways to overcome low efficiency.
Mark Turiansky, Postdoctoral Researcher, University of California, Santa Barbara
Another approach to enhancing single-photon emission involves coupling the emitters to a photonic cavity, a technique developed with the expertise of two other Quantum Foundry affiliates: computer engineering professor Galan Moody and Kamyar Parto, a graduate student in Moody’s lab.
The team aims for their model and its insights to be instrumental in designing innovative quantum emitters that will drive the quantum networks of the future.
Journal Reference:
Turiansky, M. E., et. al. (2024) Rational design of efficient defect-based quantum emitters. APL Photonics. doi:10.1063/5.0203366