Researchers Make Quantum Material Using 53-Qubit IBM Quantum Processor and Qiskit

21 december 2020

Researchers Make Quantum Material Using 53-Qubit IBM Quantum Processor and Qiskit

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An IBM Quantum Hummingbird r2 Processor (this device has 65 qubits, versus the r1’s 53 qubits) (@IBM) 

By Ryan F. Mandelbaum, Senior Technical Writer, IBM Quantum and Qiskit

A team at the University of Chicago made a quantum material called an exciton condensate using a 53-qubit IBM Quantum Hummingbird processor according to a new paper, demonstrating an exciting use for near-term quantum devices for physicists.

Condensates form when a collection of atoms or particles collapse into the same quantum state, so that quantum mechanical phenomena usually restricted to single particles can now describe the entire system. Though you’re probably most familiar with Bose-Einstein Condensates, condensates can also form from excitons, bound states of charged particles plus holes with the opposite charge, where holes are simply discrete locations in the medium that have charge due to the lack of an expected particle. The team not only succeeded in generating one of these exciton condensates on a superconducting quantum computer, but uncovered a new behavior of these materials as they formed groups of smaller condensates. This experiment demonstrates the potential power of a quantum computers to pursue problems at the forefront of physics — even today, on noisy quantum devices.

“The noise is what taught us something new,” said David Mazziotti, professor in the department of chemistry at the University of Chicago.

First predicted fifty years ago, exciton condensates are superfluids — the particle-hole pairs flow without losing any energy through friction. These superfluid properties could one day be useful for designing new wires or other more energy-efficient devices. Physicists have only recently produced these exciton condensates, and only in certain systems, like in two stacked layers of single-carbon-thick graphene sheets in a magnetic field.

Graphene bilayers are a challenging system in which to produce exciton condensates, so the University of Chicago team turned to the transmon qubits at the core of superconducting quantum computers to control the excitons. Transmons are devices where electric current oscillates near absolute zero, and the lowest two modes of the oscillation represent the zero and one state used for computation. But since these oscillators follow the rules of quantum mechanics, they can oscillate in the zero and one state simultaneously, or their oscillations can become correlated with other transmons’ oscillations. The exciton particle-hole pairing behavior acts analogously to the behavior of those transmon qubits interacting with microwave photons, and follows the same rules, giving the team a way to create a system that behaves exactly like an exciton condensate — and a way to control it.

“We have really created something that can be interpreted as an exciton condensate of photon-hole pairs,” said Mazziotti.

The team used the 53-qubit IBM Quantum Hummingbird r1 system to generate the quantum state of the condensate, first with 3 qubits (or excitons) and then with all 53 qubits. First, they applied a Hadamard gate (the superposition gate) to qubit 0, then a CNOT gate (the entangling gate) between qubits 0 and 1, 1 and 2, etc., creating the extremely entangled Greenberger–Horne–Zeilinger, or GHZ state. They looked for the signature of an exciton condensate via a large eigenvalue of the density matrix that describes the system, modified to remove other known effects that may also result in a large eigenvalue. When they calculated this modified density matrix for the system on the quantum computer, the found the telltale sign: an eigenvalue larger than 1.

As the state formed, the researchers were able to observe something not observed before: the effect of noise on a large exciton condensate. The condensate broke up into “islands of condensation,” or smaller units of exciton condensate, before dissipating completely, said LeeAnn Sager, the study’s first author and graduate student in Mazziotti’s group,

“The islands of condensation were something that neither David or I could have predicted,” said Sager. “You never know what’s going to happen with a system as you scale up larger and larger. We thought that the error might be too large — but the system was stable enough that we could observe this effect.”

The IBM Quantum team was excited to have offered access and expertise to the 53-qubit processor as part of their Academic Partner Program. “The machines we are building now will lead to powerful computation devices in the future but even now they are extremely valuable scientific instruments,” said Sebastian Hassinger, IBM Q Network Academic Partner Program lead. “Our academic partner program exists to help researchers conduct new experiments that can produce new science.”

Not only did this research demonstrate the benefits of access to early quantum devices, but also the power of an open-source software and software community supporting these systems. On top of the software’s ability to make the necessary calculations, Sager relied on the Qiskit Slack in order to get quick support while troubleshooting issues.

Quantum computers are noisy devices today that don’t have practical applications in general-purpose fields, yet. However, for physicists, even today’s computers represent the largest and most complex tests of quantum mechanics. This exciton condensate experiment demonstrates that even noisy quantum devices can be useful for those working on the forefront of physics.

“This is a great example of a creative application using our 53-qubit device,” said Jamie Garcia, Senior Manager of Quantum Applications, Algorithms, and Theory on the IBM Quantum Team. “Consistent with what we have seen in our own research, testing hypotheses on the hardware can lead to unexpected and exciting scientific results. These observations can then, in turn, inform future studies and lead to innovations in quantum computing.”

Source: Medium.com

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