Developing the next generation of quantum algorithms and materials

Simulating a quantum future.

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Current quantum computing systems are susceptible to noise and disruptive factors in the environment. This makes quantum computing noisy- resulting in loss of information in qubits by getting out of sync. This process is called Decoherence.

To overcome the limitations of current quantum computers, scientists at Pacific Northwest National Laboratory (PNNL) are developing simulations that provide a glimpse into how quantum computers work. The simulations will offer them a glimpse of the behavior of quantum systems, like qubits, their quantum states will collapse.

PNNL Computer Scientist Ang Li said, “Testing quantum algorithms on quantum devices is slow and costly. Also, some algorithms are too advanced for current quantum devices. Our quantum simulators can help us look beyond the limitations of existing devices and test algorithms for more sophisticated systems.”

Nathan Wiebe, a PNNL joint appointee from the University of Toronto, said, “Noisy quantum circuits produce errors in calculations. The more qubits needed for a calculation, the more error-prone it is.”

“This work provides a cheaper and faster way to perform quantum error correction. It potentially brings us closer to demonstrating a computationally useful example of a quantum simulation for quantum field theory on near-term quantum hardware.”

Physicist Ben Loer and his colleagues look to the environment to manage external noise sources, whereas Wiebe works to limit noise by developing algorithms for error correction.

Lover’s background in achieving ultra-low levels of natural radioactivity, which is required to look for experimental evidence of dark matter in the cosmos, is used to prevent qubit decoherence.

Loer said, “Radiation from the environment, such as gamma rays and X-rays, exists everywhere. Since qubits are so sensitive, we had an idea that this radiation may be interfering with their quantum states.”

To test this, Loer, project lead Brent VanDevender, and colleague John Orrell teamed up with scientists at the Massachusetts Institute of Technology (MIT) and MIT’s Lincoln Laboratory and used a lead shield to protect qubits from radiation. They designed the shield for use within a dilution refrigerator—a technology used to produce the just-above-absolute-zero temperature necessary for operating superconducting qubits. They saw that qubit decoherence decreased when the qubits were protected.

Although, this is the first step to understanding how radiation affects quantum computing. Loer plans to look at how radiation disturbs circuits and substrates within a quantum system.

Loer is taking his lead-shielded dilution refrigerator research underground in PNNL’s Shallow Underground Laboratory with the help of PNNL Chemist Marvin Warner.

Warner said, “If we develop a quantum device that doesn’t perform as it should, we need to be able to pinpoint the problem. By shielding qubits from external radiation, we can start to characterize other potential sources of noise in the device.”

James (Jim) Ang, the chief scientist for computing, said, “PNNL’s cultivation of both industry and university collaborations are building a foundation for quantum computing in the Pacific Northwest that sets the stage for future hybrid classical-quantum computing.”