To build a universal quantum computer from fragile quantum components, effective implementation of quantum error correction (QEC) is an essential requirement and a central challenge. QEC is used in quantum computers, which have the potential to solve scientific problems beyond the scope of supercomputers, to protect quantum information from errors due to various types of noise.

Published by the magazine Nature, research written by University of Massachusetts Amherst physicist Chen Wang, graduate students Jeffrey Gertler and Shruti Shirol, and postdoctoral researcher Juliang Li take a step toward building a fault-tolerant quantum computer. They have realized a new type of QEC in which the quantum errors are spontaneously corrected.

Today’s computers are built with transistors that represent classic bits (zeros or ones). Quantum computing is an exciting new computational paradigm using quantum bits (qubits) where quantum superposition can be exploited for exponential gains in processing power. Fault-tolerant quantum computing can greatly advance the discovery of new materials, artificial intelligence, biochemical engineering, and many other disciplines.

Since qubits are intrinsically fragile, the most salient challenge in building such powerful quantum computers is an efficient implementation of quantum error correction. Existing demonstrations of QEC are active, which means that they should be periodically checked for errors and fixed immediately, which is very demanding on hardware resources and therefore hinders the scaling-up of quantum computers.

In contrast, the researchers’ experiment achieved passive QEC by adjusting the friction (or dissipation) experienced by the qubit. Since friction is widely regarded as the nemesis of quantum coherence, this result can seem quite surprising. The trick is that the dissipation has to be specifically designed in a quantum way. This general strategy has been known in theory for about two decades, but a practical way to obtain such dissipation and put it to use for QEC has been challenging.

“While our experiment is still a fairly rudimentary demonstration, we have finally fulfilled this counterintuitive theoretical possibility of dissipative QEC,” said Chen. “Looking ahead, the implication implies that there may be more options to protect our qubits from errors and do so less costly. Therefore, this experiment raises the prospects for potentially building a usable error-tolerant quantum computer in the medium to long term.”

Chen describes in layman’s terms how strange the quantum world can be. As in the famous (or infamous) example of German physicist Erwin Schrödinger, a cat packed in a closed box can be dead or alive at the same time. Every logical qubit in our quantum processor is very similar to a mini Schrödinger’s cat ., we literally call it a “cat qubit.” Having many such cats can help us solve some of the most difficult problems in the world.

“Unfortunately it is very difficult to keep a cat like this, as gas, light or anything else that leaks into the bowl will destroy the magic: the cat will die or just a regular live cat,” Chen explains. “The simplest strategy to protect a Schrodinger’s cat is to make the box as tight as possible, but that also makes it more difficult to use for calculations. What we just showed was similar to putting it on a special way of painting the inside of the box. that somehow helps the cat to better survive the inevitable damage from the outside world. ”

To build a universal quantum computer from fragile quantum components, effective implementation of quantum error correction (QEC) is an essential requirement and a central challenge. QEC is used in quantum computers, which have the potential to solve scientific problems beyond the scope of supercomputers, to protect quantum information from errors due to various types of noise.

Published by the magazine Nature, research written by University of Massachusetts Amherst physicist Chen Wang, graduate students Jeffrey Gertler and Shruti Shirol, and postdoctoral researcher Juliang Li take a step toward building a fault-tolerant quantum computer. They have realized a new type of QEC in which the quantum errors are spontaneously corrected.

Today’s computers are built with transistors that represent classic bits (zeros or ones). Quantum computing is an exciting new computational paradigm using quantum bits (qubits) where quantum superposition can be exploited for exponential gains in processing power. Fault-tolerant quantum computing can greatly advance the discovery of new materials, artificial intelligence, biochemical engineering, and many other disciplines.

Since qubits are intrinsically fragile, the most salient challenge in building such powerful quantum computers is an efficient implementation of quantum error correction. Existing demonstrations of QEC are active, which means that they should be periodically checked for errors and fixed immediately, which is very demanding on hardware resources and therefore hinders the scaling-up of quantum computers.

In contrast, the researchers’ experiment achieved passive QEC by adjusting the friction (or dissipation) experienced by the qubit. Since friction is widely regarded as the nemesis of quantum coherence, this result can seem quite surprising. The trick is that the dissipation has to be specifically designed in a quantum way. This general strategy has been known in theory for about two decades, but a practical way to obtain such dissipation and put it into use for QEC has been challenging.

“While our experiment is still a rather rudimentary demonstration, we have finally fulfilled this counterintuitive theoretical possibility of dissipative QEC,” said Chen. “Looking ahead, the implication implies that there may be more options to protect our qubits from errors and do so less costly. Therefore, this experiment raises the prospects for potentially building a usable error-tolerant quantum computer in the medium to long term.”

Chen describes in layman’s terms how strange the quantum world can be. As in the famous (or infamous) example of German physicist Erwin Schrödinger, a cat packed in a closed box can be dead or alive at the same time. Every logical qubit in our quantum processor is very similar to a mini Schrödinger’s cat We quite literally call it a “cat qubit.” Having many such cats can help us solve some of the most difficult problems in the world.

“Unfortunately it is very difficult to keep a cat like this, as gas, light or anything else that leaks into the bowl will destroy the magic: the cat will die or just a regular live cat,” Chen explains. “The simplest strategy to protect a Schrodinger’s cat is to make the box as tight as possible, but that also makes it more difficult to use for calculations. What we just showed was similar to putting it on a special way of painting the inside of the box. that somehow helps the cat to better survive the inevitable damage from the outside world. ”