A Duke Kunshan student-professor team has produced a ground-breaking quantum physics study that expands understanding of the concept of frustration.
Their research, which will be published in top tier science publication Physical Review Letters, could be used to produce algorithms for quantum computers, a burgeoning technology that harnesses the laws of quantum mechanics to solve problems too complex for classical computers.
“Frustration makes us think outside the box to resolve contradicting demand from multiple facets of our lives,” said Myung-Joong Hwang, assistant professor of physics at DKU and corresponding author of the study, titled ‘Frustrated Superradiant Phase Transition’.
“The same is true in physics. A complex system gets ‘frustrated’ when it is subject to competing constraints that cannot be simultaneously satisfied and is forced to do something clever to find a compromised solution. As a result, there often emerge exotic and surprising collective behaviors,” he added.
The physics of frustration has been studied at length in interacting spin systems where each spin has a binary choice for its direction, either up or down. In this case, it is straightforward to make them frustrated by demanding that all neighboring spins move in the opposite direction, a requirement that cannot be satisfied for spins placed on a triangle.
Written with first author Jinchen Zhao, an undergraduate at Duke Kunshan, the research paper expands the concept of frustration to photons, something that has never been done before.
Photons, which are a quantum unit of electromagnetic radiation, such as radio waves, X-rays, and light, on their own cannot be frustrated; two beams of light will simply pass through each other. However, when mixed with matter they interact to form a new state called superradiant phase, where the two are entangled. In this state photons can interact with each other and become frustrated.
The paper looks at a triangular model of three sites containing photons in superradiant phase, where photons from each site can leak into the neighboring ones. As photons are waves they can be in a positive (up) or negative (down) phase. If each site is forced to have the opposite sign to its neighbours this creates an impossible situation, which frustrates the photons as they meet each other.
Unable to satisfy the demand to have the opposite phase to their neighbours, the study found that the frustrated photons instead compromise to form every potential state simultaneously, which with three sites is six states.
This existence of all potential states at the same time, called quantum superposition, is the essence of quantum physics, and the basis of quantum computers. Imagine a traditional computer works in one state, while a quantum computer, with a billion sites, could work in multiple billions of states simultaneously, giving it much greater computational power. Such computers could have practical uses across a range of industries, such as pharmaceuticals and artificial intelligence, as well as theoretical scientific uses in running quantum models that are too large for traditional computers.
The discovery “paves the way for the exploration of frustrated phases of coupled light and matter,” said Zhao.
“We hope to see it can be realized by various quantum technologies like superconducting circuits, trapped ions or cold atoms,” which are used in the development of quantum computers, he said.
For the next stage of research the pair will explore how frustrated photons behave in greater detail, as well as developing quantum algorithms, problem solving instructions designed to run on a quantum computer, he added.
