There are also quantum bits, or qubits, which have a critical difference from ordinary bits and bytes. These photons – particles of light – can carry quantum information and offer extraordinary abilities that cannot be achieved in any other way. Unlike binary computing, where bits can only represent 0 or 1, the behavior of qubits is in the realm of quantum mechanics. Through “superposition”, a qubit can represent 0, 1, or any proportion in between. This greatly increases the processing speed of quantum computers compared to today’s computers.
“Learning about what qubits are capable of has been a driving force for the emerging field of quantum technology, opening up new and unexplored applications such as quantum communications, computing and sensing,” said Hong Koo Kim, Professor of Electrical and Computer Engineering at the University of Pittsburgh’s Swanson School of Engineering.
Quantum technology is important for a number of fields, such as for banks protecting financial information or giving researchers the speed needed to mimic all aspects of chemistry. And through quantum “entanglement,” qubits can “communicate” across vast distances as a single system. Kim and his graduate student, Yu Shi, make a discovery that could help quantum technology make a quantum leap.
It starts with one photon
Photon-based quantum technologies rely on a single photon source that can emit individual photons.
These single photons can be generated from nanometer-scale semiconductors, better known as quantum dots. Similar to how microwave antennas broadcast cell phone signals, the quantum dot acts as an antenna emitting light.
“By conducting careful analysis, we found that the quantum dot emitter – or nanometer-scale dipole antenna – traps a large amount of energy,” explains Kim. “The operation of the outer regime of the dipole emitter is well understood, but this is really the first time that a dipole has been studied inside.”
The photons from those quantum dots appear right-handed, much like how can we be right-handed or left-handed. Quantum information is carried by these left-handed individual photons. Thus, sorting them into different paths is an important task for quantum information processing. Kim’s team has developed a new way to separate photons with different hands and efficiently harvest them for further processing.
“Findings from this work are expected to contribute to developing a high-speed single photon source, an essential component required in quantum photonics,” said Kim.
The paper, “Spin texture and chiral coupling of circularly polarized dipole fields,” is published in the journal, Nanophotonics. This work was funded by the Office of Naval Research. (DOI:10.1515/nanoph-2022-0581)