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“Superposition”
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A duet between a singer and a quantum processor highlights the potential of quantum computing

There have been some great duets in history: Sonny and Cher. Michael Jackson and Paul McCartney. Beyoncé and Jay Z. David Bowie and Queen. Recently, there was a unique duet that occurred between a singer in the UK and a rather solid Angeleno — and we’re not talking about the duet between James Corden and Adele on “Carpool Karaoke.”

Rather, for first time in history there was a live duet between a Welsh mezzo-soprano and a cold black box 5,351 miles away — a quantum information processor.

Alexis Kirke, a composer and senior research fellow in music at the Interdisciplinary Centre for Computer Music Research at Plymouth University, partnered with Daniel Lidar, scientific and technical director of the USC–Lockheed Martin Quantum Computing Center at the Information Sciences Institute (ISI), to create a unique experience: the first live artistic performance using a quantum computer.

The performance took place at the Port Eliot Festival in the UK, which featured the likes of Kim Gordon of Sonic Youth, global DJ Erol Alkan and feminist Gloria Steinem.

For this project, Kirke asked soprano Juliette Pochin, whose credits include “The Lord of the Rings,” “Star Wars” and “Harry Potter” films, to sing a duet with the 1098-qubit D-Wave Two quantum processor, housed at USC’s ISI in Marina Del Rey, California.

Quantum computers encode data in quantum bits, or “qubits,” that have the capability to represent the two digits of one and zero at the same time (as opposed to traditional bits, which can encode distinctly either a one or a zero). This property, called superposition, is what may one day allow quantum computers to perform optimization calculations much faster than is possible using traditional computers, as they can process and produce a multitude of solutions at the same time. Not surprisingly then, Kirke named his 15-minute piece, “Superposition.”

The three-part performance is based on the Greek mythological figure Niobe. Kirke chose this particular story based on the fact that the D-Wave quantum processor contains the metal niobium. The performance also featured words from “Hamlet,” a play that references Niobe, interspersed with terms from quantum computing. It was developed while Kirke did a two-week residency at USC during spring 2016.

“I wanted the public to listen to what is most human,” Kirke said. “Opera, this classical movement, throws into sharp relief the difference between the human form of communication and the quantum computer, an alien, mysterious technology. Quantum computing is the ultimate alien in technology at the moment.”

On July 29, as Pochin sang, the sounds of her voice were captured by a microphone and sent via the internet to the quantum processor at ISI. Using its 1098 qubits, the processor responded to Pochin’s harmony based on algorithms created by Kirke. These responses from the lab were transferred to a laptop and speaker in the same room with Pochin back at the festival. A second “subsystem” generated non-pitched noises of different lengths, roughness and loudness, to illustrate the concept of quantum entanglement, in which particles are stuck together in pairs.

“Music has a very natural [way] of saying multiple things at the same time — it’s called a chord,” said Kirke. “It is much harder to do with a poem.”

The concept of superposition can be difficult for the public to understand, which is why Kirke was eager to illustrate it, and Lidar eager to help.

It is important, said Lidar, “to involve the general public in our scientific activities in a manner that is meaningful and understandable to all. I can’t think of a better way to do this than via an artistic rendering. When you play different notes together, it’s of course not a genuine quantum superposition, but it’s a good analogy that can be grasped intuitively.”

Yet Lidar doesn’t want just to help the public understand the concept of superposition. He wants quantum computers to explore the limits of computation and at the same time become useful tools for society. By design, quantum computers might be a boon to cryptologists who want to break previously unbreakable codes, or researchers who simultaneously anticipate and model a vast number of chemical reactions to bring new drugs or materials to market more quickly. Superposition and quantum optimization could speed up the pace of the solutions the world needs, enhancing machine learning and addressing big data problems, improving image recognition and classification, and detecting anomalies or even stock portfolio optimization.

Lidar’s lab is among a rapidly growing group around the world that studies how quantum mechanics can be used to supercharge computation and information processing. He and fellow researchers Walter Vinci and Tameem Albash recently published an article in the journal “Nature Quantum Information,” in which they solved some of the challenges of creating and maintaining quantum superpositions.

“While superposition — along with the ability of quantum states to ‘interfere’ (cancel or reinforce each other like waves in a pond) and ‘tunnel’ through energy barriers — is what may one day allow quantum processors to ultimately perform optimization calculations much faster than is possible using traditional processors, exactly because of the exotic way in which quantum computers process information, they are highly sensitive to errors of different kinds,” explained Lidar. “When such errors occur, they can erase any quantum computational advantage. Therefore, developing methods to overcome errors is of paramount importance in the quest to demonstrate ‘quantum supremacy.’”

Lidar, Vinci and Albash have developed a new method to suppress heating errors, as temperature is a big source of errors in these types of devices. Their solution, which they call nested quantum annealing correction, couples several qubits together on a D-Wave Two quantum optimizer. Without changing the hardware, these qubits act effectively as one qubit, which experiences a lower temperature. Thus, they are minimizing the effect of heating as a source of noise or error. Furthermore, this error-correction is implementable not only on platforms such as the D-Wave processor on which it was tested, but also on other future quantum optimization devices with different hardware architectures.

This, said Lidar, “gets us much closer to practical applications with real-world relevance.”

While this quantum reality might take some time to come to fruition, experiments like the “Superposition” performance give the public a greater understanding of quantum mechanics and the potential of quantum computing for humanity.