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In experiments performed at the University of Wisconsin-Madison, researchers found that fluctuations in the electrical charge of multiple quantum bits, or qubits, can be highly correlated, as opposed to completely random and independent. The team also linked tiny error-causing perturbations in the qubits charge state to the absorption of cosmic rays. Credit: Illustration courtesy of UW-Madison

Research by aLawrence Livermore National Laboratory(LLNL) physicist and a host of collaborators is shedding new light on one of the major challenges to realizing the promise and potential of quantum computing error correction.

In a new paperpublished inNatureand co-authored by LLNL physicist Jonathan DuBois, scientists examined quantum computing stability, particularly what causes errors and how quantum circuits react to them. This must be understood in order to build a functioning quantum system. Other co-authors included researchers at theUniversity of Wisconsin-Madison,Fermi National Accelerator Laboratory, Google,Stanford Universityand international universities.

In experiments performed at UW-Madison, the research team characterized a quantum testbed device, finding that fluctuations in the electrical charge of multiple quantum bits, or qubits the basic unit of a quantum computer can be highly correlated, as opposed to completely random and independent. When a disruptive event occurs, such as a burst of energy coming from outside the system, it can affect every qubit in the vicinity of the event simultaneously, resulting in correlated errors that can span the entire system, the researchers found. Additionally, the team linked tiny error-causing perturbations in the qubits charge state to the absorption of cosmic rays, a finding that already is impacting how quantum computers are designed.

For the most part, schemes designed to correct errors in quantum computers assume that the errors across qubits are uncorrelated theyre random. Correlated errors are very difficult to correct, said co-author DuBois, who heads LLNLs Quantum Coherent Device Physics (QCDP) Group. Essentially, what this paper is showing is that if a high-energy cosmic ray hits the device somewhere, it has the potential to affect everything in the device at once. Unless you can prevent that from happening you cant perform error correction efficiently, and youll never be able to build a working system without that.

Unlike bits found in classical computers, which can exist only in binary states zeroes or onesthe qubits that make up a quantum computer can exist in superpositions. For a few hundred microseconds, data in a qubit can be either a one or zero before being projected into a classical binary state. Whereas bits are only susceptible to one type of error, under their temporary excited charge state, the delicate qubits are susceptible to two types of error, stemming from changes that can occur in the environment.

Charged impulses, even minute ones like those from cosmic rays absorbed by the system, can create a blast of (relatively) high-energy electrons that can heat up the quantum devices substrate just long enough to disrupt the qubits and disturb their quantum states, the researchers found. When a particle impact occurs, it produces a wake of electrons in the device. These charged particles zoom through the materials in the device, scattering off atoms and producing high-energy vibrations and heat. This alters the electric field as well as the thermal and vibrational environment around the qubits, resulting in errors, DuBois explained.

Weve always known this was possible and a potential effectone of many that can influence the behavior of a qubit, DuBois added. We even joked when we saw bad performance that maybe its because of cosmic rays. The significance of this research is that, given that sort of architecture, it puts some quantitative bounds on what you can expect in terms of performance for current device designs in the presence of environmental radiation.

To view the disruptions, researchers sent radio frequency signals into a four qubit system and, by measuring their excitation spectrum and performing spectroscopy on them, were able to see the qubits flip from one quantum state to another, observing that they all shift in energy at the same time, in response to changes in the charge environment.

If our model about particle impacts is correct, then we would expect that most of the energy is converted into vibrations in the chip that propagate over long distances, said UW-Madison graduate student Chris Wilen, the papers lead author. As the energy spreads, the disturbance would lead to qubit flips that are correlated across the entire chip.

Using the method, researchers also examined the lifetimes of qubits the length of time that qubits can remain in their superposition of both one and zero and correlated changes in the charge state with a reduction in lifetime of all the qubits in the system.

The team concluded that quantum error correction will require development of mitigation strategies to protect quantum systems from correlated errors due to cosmic rays and other particle impacts.

I think people have been approaching the problem of error correction in an overly optimistic way, blindly making the assumption that errors are not correlated, said UW-Madison physics professor Robert McDermott, senior author on the study. Our experiments show absolutely that errors are correlated, but as we identify problems and develop a deep physical understanding, were going to find ways to work around them.

Though long theorized, DuBois said the teams findings had never been experimentally proven in a multi-qubit device before. The results will likely impact future quantum system architecture, such as putting quantum computers behind lead shielding or underground, introducing heatsinks or dampers to quickly absorb energy and isolate qubits, and alter the types of materials used in quantum systems.

LLNL currently has aquantum computing testbed system, designed and built with funding from a Laboratory Directed Research and Development (LDRD) Strategic Initiative that began in 2016. It is being developed with continued support by the National Nuclear Security Administrations Advanced Simulation & Computing program and its Beyond Moores Law project.

In related follow-on work, DuBois and his team in the QCDP group are studying a quantum device that is significantly less sensitive to the charge environment. At the extreme cold temperatures required by quantum computers (systems are kept at temperatures colder than outer space), DuBois said researchers observe that thermal and coherent energy transport is qualitatively different from room temperature. For example, instead of diffusing, thermal energy can bounce around in the system like sound waves.

DuBois said he and his team are focused on understanding the dynamics of the microscopic explosion that occurs inside quantum computing devices when they interact with high energy particles and developing ways to absorb the energy before it can disrupt the delicate quantum states stored in the device.

There are potentially ways to design the system so its as insensitive as possible to these kinds of events, and in order to do that you need to have a really good understanding of how it heats up, how it cools down and what exactly is happening through the whole process when exposed to background radiation, DuBois said. The physics of whats going on is quite interesting. Its a frontier, even aside from the quantum applications, because of the oddities of how energy is transported at those low temperatures. It makes it a physics challenge.

DuBois has been working with the papers principal investigator McDermott (UW-Madison)and his group to develop ways to use qubits as detectors to measure charge bias, the method the team used in the paper to conduct their experiments.

Reference: Correlated charge noise and relaxation errors in superconducting qubits by C. D. Wilen, S. Abdullah, N. A. Kurinsky, C. Stanford, L. Cardani, G. DImperio, C. Tomei, L. Faoro, L. B. Ioffe, C. H. Liu, A. Opremcak, B. G. Christensen, J. L. DuBois and R. McDermott, 16 June 2021, Nature.DOI: 10.1038/s41586-021-03557-5

The featured work, including DuBois contribution, was funded by a collaborative grant between LLNL and UW-Madisonfrom the U.S.Department of Energys Office of Science.

The paper included co-authors from UW-Madison, the Fermi National Accelerator Laboratory, the Kavli Institute for Cosmological Physics at the University of Chicago, Stanford University, INFN Sezione di Roma, Sorbonne Universites Laboratoire de Physique Theorique et Hautes Energies and Google.

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Experiments Prove Quantum Computing Errors Correlated, Tied to Cosmic Rays - SciTechDaily

Bitcoin and cryptocurrencies have seen a huge resurgence over the last year following the brutal so-called crypto winter that began in 2018.

The bitcoin price has this year climbed to never-before-seen highs, topping $60,000 per bitcoin before falling back slightly. Other smaller cryptocurrencies have risen at an even faster clip than bitcoin, with many making percentage gains into the thousands.

Now, as bitcoin and cryptocurrencies begin to carve out a place among traditional assets in investor portfolios, technologists have warned that advances in quantum computing could mean the encryption that underpins bitcoin is "fundamentally" undermined as soon as 2026unless the software is updated.

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The bitcoin price has risen many hundreds of percent over the last few years but quantum computing ... [+] could spell the end of bitcoin and cryptocurrencies unless urgent action is taken.

"Quantum computers, expected to be operational by around 2026, will easily undermine any blockchain security systems because of their power," says the founder of quantum encryption company Arqit, David Williams, speaking over the phone. Arqit is gearing up for a September SPAC listing in New York.

"There needs to be rather more urgency," Williams adds.

Quantum computing, which sees traditional computer "bits" replaced with quantum particles (qubits) that can calculate information at vastly increased speed, has been in development since the 1990s. Researchers at universities around the world are now on the verge of creating a working quantum computer, with search giant Google and scientists from the University of New South Wales in Sydney, Australia, recently making headlines with breakthroughs.

Williams, pointing to problems previously identified by the cofounder of ethereum and creator of cardano, Charles Hoskinson, warns that upgrading to post-quantum algorithms will "dramatically slow blockchains down" and called for blockchain developers to adopt so-called quantum encryption keys.

"Blockchains are effectively fundamentally flawed if they dont address the oncoming quantum age. The grownups in the room know what's coming."

Others have also begun working on getting bitcoin and other blockchains ahead of quantum computing.

"If this isn't addressed before quantum computers pose a threat, the impact would be massive," says Duncan Jones, head of quantum cybersecurity at Cambridge Quantum Computing, speaking via email. "Attackers could create fraudulent transactions and steal currency, as well as potentially disrupting blockchain operations."

Earlier this month, Cambridge Quantum Computing, along with the Inter-American Development Bank and Tecnolgico de Monterrey, identified four potential threats to blockchain networks posed by quantum computers and used a post-quantum cryptography layer to help protect them.

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"Time is of the essence here," says Jones, pointing to Google chief executive Sundar Pichai's prediction that encryption could be broken in as little as five to 10 years. "It's important for decentralized networks to start this migration process soon because it requires careful planning and execution. However, I'm hopeful the core developers behind these platforms understand the issues and will be addressing them."

Recently, it's been reported that China is pulling ahead in the global quantum race, something Williams fears could undermine both traditional and crypto markets to the same degree as the 2008 global financial crisis.

"On day one, the creation of a quantum computer doesn't break everything," says Williams. "It will probably initially happen in secret and the information will slowly leak out that the cryptography has been broken. Then there will be a complete loss of confidence, similar to how the global financial crisis saw confidence in the system disintegrate."

With more than 11,000 different cryptocurrencies now listed on crypto data website CoinMarketCap and competition between bitcoin and other major cryptocurrencies reaching fever pitch, adding protection against the coming quantum revolution could be beneficial.

"If any one blockchain company could deliver proof it's quantum-safe it would have an advantage," says Williams.

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Urgent Warning Issued Over The Future Of Bitcoin Even As The Crypto Market Price Smashes Past $2 Trillion - Forbes

The U.S. Department of Energy (DOE) has announced $61 million in funding for infrastructure and research projects to advance quantum information science (QIS).

Specifically, the DOE is supplying $25 million in funding for creating quantum internet testbeds, which will advance foundational building blocks including devices, protocols, technology, and techniques for quantum error correction at the internet scale.

The DOE also is providing $6 million in funding for scientists to study and develop new devices to send and receive quantum network traffic and advance a continental-scale quantum internet.

Lastly, the DOE granted $30 million of funding to five DOE Nanoscale Science Research Centers to support cutting-edge infrastructure for nanoscience-based research to strengthen the United States competitiveness in QIS and enable the development of nanotechnologies.

Harnessing the quantum world will create new forms of computers and accelerate our ability to process information and tackle complex problems like climate change, said U.S. Secretary of Energy Jennifer M. Granholm in a statement. DOE and our labs across the country are leading the way on this critical research that will strengthen our global competitiveness and help corner the markets of these growing industries that will deliver the solutions of the future.

The DOE recognized the advantages of QIS back in 2018 when it became an integral partner in theNational Quantum Initiative, which became law in December 2018. Since then, the DOE Office of Science has launched a range of multidisciplinary research programs in QIS, including developing quantum computers as testbeds, designing new algorithms for quantum computing, and using quantum computing to model fundamental physics, chemistry, and materials phenomena.

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Energy Department Sets $61M of Funding to Advance QIS Research - MeriTalk