Study by Lawrence Livermore National Laboratory (LLNL) Physicists and many collaborators shed new light on error correction, one of the key challenges in realizing the potential and potential of quantum computing.
In a new treatise Published in Nature Scientists co-authored by LLNL physicist Jonathan DuBois have investigated the stability of quantum computing, especially the causes of errors and how quantum circuits react to them. You need to understand this in order to build a working quantum system. For other co-authors, University of Wisconsin-Madison, Fermi National Accelerator Laboratory,Google, Stanford University And an international university.
In an experiment conducted at UW-Madison, the research team characterized the quantum testbed device, and the charge fluctuations of multiple qubits or “qubits”, which are the basic units of quantum computers, are completely random and independent. doing. Catastrophic events, such as bursts of energy from outside the system, can affect all cubics near the event at the same time, resulting in potentially system-wide correlation errors. The researcher discovered. In addition, the team associated perturbations that cause small errors in the charge state of qubits with cosmic ray absorption. This is a discovery that has already influenced the way quantum computers are designed.
“In most cases, schemes designed to correct quantum computer errors assume that errors between qubits are uncorrelated. They are random. Correcting correlated errors is very much. It’s difficult, “said DuBois, co-author of LLNL’s Quantum Coherent Device Physics (QCDP) group. “In essence, this paper shows that if a high-energy cosmic ray hits somewhere in the device, it can affect everything in the device at once. It can be prevented. Without it, error correction cannot be performed efficiently, and without it, a system that works cannot be built. “
Unlike the bits found in classical computers, which can only exist in the binary state (0 or 1), the qubits that make up a quantum computer can exist in superposition. For hundreds of microseconds, the data in the qubit will be either 1 or 0 before being projected into the classical binary state. Bits are susceptible to one type of error, whereas in transient excited state states, delicate cubits are susceptible to two types of errors due to changes that may occur in the environment. I will.
Charged impulses, even tiny ones such as from cosmic rays absorbed by the system, can heat the substrate of the quantum device to destroy the qubits and disturb the quantum state (relatively) high energy. It can cause an electron explosion. Discovered by researchers. When particle collisions occur, electron wakes occur in the device. These charged particles zoom the material inside the device, scattering atoms and producing high-energy vibrations and heat. This changes the thermal and oscillating environment around the electric and cubits, causing errors, DuBois explained.
“We’ve always known that this is possible and has potential implications, and it’s one of many issues that can affect the behavior of qubits,” DuBois added. “We joked when we saw the bad performance that cosmic rays might have caused. The importance of this study is that given the architecture, the current device design in the presence of environmental radiation. Putting some quantitative limits on what you can expect in terms of performance. “
To confirm the confusion, researchers send radio frequency signals to a 4-qubit system, measure the excitation spectrum, and perform spectroscopy to move the qubit from one quantum state to another. I confirmed that it was “reversed”. At the same time, energy as the charging environment changes.
“If the model for particle impact is correct, most of the energy is expected to be converted into vibrations in the chip and propagate over long distances,” said Chris Willen, a graduate student at UW-Madison, the lead author of the paper. Says. “As the energy spreads, the disturbance leads to a qubit flip that correlates across the chip.”
Using this method, researchers also examine the lifetime of qubits (the length of time that qubits can stay in both superpositions of 1 and 0) and change the charge state of everything in the system. Correlated with the decrease in qubit life.
The team concluded that quantum error correction requires the development of mitigation strategies to protect quantum systems from correlation errors due to the effects of cosmic rays and other particles.
“I think people are tackling the problem of error correction in an overly optimistic way, blindly assuming that the errors are uncorrelated,” said UW-Madison Physics, senior author of the study. Professor Robert McDermott said. “Our experiments absolutely show that the errors are correlated, but as we identify the problems and gain a deeper physical understanding, we will find ways to avoid them.”
After a long theory, DuBois says the team’s findings have never been experimentally proven on multi-cubit devices. The result is that quantum computers can be placed in lead shields or underground, heat sinks and dampers can be introduced to quickly absorb energy to separate qubits, and the types of materials used in quantum systems can be changed. It may affect the future quantum system architecture.
LLNL is now Quantum computing testbed systemWas designed and built with funding from the Laboratory Directed Research and Development (LDRD) Strategic Initiative, which was launched in 2016. It is being developed with the continued support of the National Nuclear Security Administration’s Advanced Simulation & Computing program and its Beyond Moore’s Law project.
In a related subsequent work, DuBois and his team in the QCDP group are studying quantum devices that are significantly less sensitive to the charge environment. At the extremely low temperatures required by quantum computers (the system is kept cooler than space), Dubois observes that heat and coherent energy transport is qualitatively different from room temperature. Said that. For example, instead of diffusing heat energy, it can bounce back in the system like a sound wave.
Dubois and his team understand the dynamics of “microscopic explosions” that occur when quantum computing devices interact with high-energy particles, before destroying the delicate quantum states stored in the devices. He said he is focusing on developing ways to absorb energy. ..
“There are potential ways to design a system to be as unaffected by these types of events as possible. To do so, see how the system is heated, cooled, and exactly what is happening. It needs to be fully understood, throughout the process when exposed to background radiation, “says DuBois. “The physics of what’s happening is very interesting. Aside from quantum applications, it’s a frontier because of the strangeness of how energy is transported at these low temperatures. It’s that. I will make it a physics challenge. “
DuBois worked with the paper’s lead researcher McDermott (UW-Madison) and his group to develop a method for using qubits as detectors to measure charge bias. This is the method the team used to experiment with the treatise.
Featured works, including the contribution of DuBois, were funded by a joint grant between LLNL and UW-Madison in the United States. Department of Energy Science..
This paper included co-authors of UW-Madison, Fermi National Accelerator Laboratory, Kavli Institute for Cosmological Physics at the University of Chicago, Stanford University, INFN Sezione di Roma, Laboratoire de Physique Theorique et Hautes Energies at Sorbonne Universite, and Google. ..
New research proves that quantum computational errors are correlated and connects them to cosmic rays
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