- Purdue University researchers have developed a quantum computing technique that utilizes entangled photons (or qudits) instead of qubits
Purdue University researchers have developed a quantum computing technique that utilizes entangled photons (or qudits) instead of qubits. And the key advantage of the technique is that it allows quantum computing to be done at room temperature. This technology could enable computers to search through data at speeds beyond that of conventional computers.
In a statement, a spokesperson at Purdue wrote that the laws of random walks are fundamentally different in the quantum realm. And a quantum agent can move to the right and left simultaneously at each step. This means that a quantum particle can travel in several trajectories at the same time — which can lead to searches of large-scale databases much faster.
“We like to refer to this as the quantum walk of the rainbow,” said Andrew Weiner, Purdue University’s Scifres Family Distinguished Professor of Electrical and Computer Engineering while discussing the techniques involved in using photons at specific colors. “One major advantage is that, unlike other types of quantum computing, this technique can be done at room temperature.”
The technology can be also used to experiment with what can be done with integrated photonics and other components common in lightwave or optical communication — which could reduce cost and bring compatibility with fiber optics communications infrastructure.
“In the future, quantum walks could be used to search through massive amounts of data in a reasonable time,” added Weiner. “This might include quickly searching through all of the world’s fingerprints or finding a microscopic defect in a newly manufactured airplane wing or defects in microprocessors.”
Last year, Google revealed the results of a quantum supremacy experiment using the 53-qubit processor called “Sycamore.” The researchers pointed out that while this was a dramatic achievement, quantum computing using qubits has its challenges. For example, quantum computers need to be cooled to near absolute zero — which is best expressed on the Kelvin temperature scale in order to maintain the superposition of the qubits.
“The superconducting quantum circuit works at about 20 degrees milli-Kelvin. So, it’s a huge, very complex refrigerator that allows the qubits to store the quantum information and act in a quantum way,” explained Weiner. “We’re using photons instead of superconducting qubits, which allows our work to be done at room temperature. To be fair, photons have their challenges as well, and cannot yet rival the complexity of operations achieved with superconducting qubits.
Quantum walks are a central part of the development of quantum computers. And there is another way of doing quantum walks but at room temperature using photons in a way that has not been tapped into before.
The photons used in this technique walk in the color (i.e., frequency) space and randomly changes colors in a quantum manner during the walk. And the photons come in highly entangled pairs such that the walking pattern of one photon is highly dependent on how the other twin photon walks.
By programming the quantum state, the photons can walk in an attractive or repulsive way. And such photons can also store and process multivalued quantum information known as qudits. Last year, Weiner and postdoctoral researcher Poolad Imany (who is now a postdoctoral associate at the National Institute of Standards and Technology) announced that they had created a two-qudit gate, which would be the equivalent to a transistor in conventional computing.
Random walking (using computer bits) is analogous to a coin flip because bits have values of either 1 or 0 said Weiner. The movement of the walker (a step to the right or left) is then dependent on the outcome of this coin flip.
However, quantum walking using qudits is comparable to throwing a six-sided die. In this case, the entangled photons were the equivalent of an eight-sided die like the type used in Dungeons and Dragons. And qudits bring the potential for placing more information on each photon and exploring more quantum random walk outcomes in parallel.
“Previously, changing the evolution time of photons required changing the physical size of the quantum walk circuit. In this case, there is no abrupt step where the particle jumps to multiple positions. It just continuously ‘leaks’ to multiple positions with a walking-depth that can be electrically tuned,” he said. “This is especially important because this is how natural phenomena evolve. Consequently, continuous quantum walks are especially well-suited to the simulation of quantum phenomena like molecular dynamics,” commented Imany.
This work was supported in part by the National Science Foundation under award number 1839191-ECCS. And this discovery was published in Science Advances.
Featured photo credit: Purdue University
