Ushering in a new era of fault-tolerant quantum computing! World's First Logic Quantum Bit Circuit Realizes Error-Free Computing

The implementation of a programmable quantum processor based on encoded logic quantum bits running up to 280 physical quantum bits is reported in a paper distributed within QuEra.

The collaborators report the following key achievements:

- Creation and entanglement of the largest logic quantum bits to date, showing a code distance of 7, which enables detection and correction of arbitrary errors that occur during the operation of entangled logic gates (the larger the code distance, the greater the resistance to quantum errors). Furthermore, it was shown for the first time that increasing the code distance can indeed reduce the error rate in logic operations.

- Forty-eight small logic quantum bits for executing complex algorithms were implemented, and their performance exceeded that of the same algorithms when executed using physical quantum bits.

- By controlling 280 physical bits, 40 medium-sized error-correcting codes were constructed.

These results herald the arrival of early error-correcting quantum computing and point the way to the development of large-scale logic processors.

The implementation of a programmable quantum processor based on encoded logic quantum bits running up to 280 physical quantum bits is reported in a paper distributed within QuEra.

The collaborators report the following key achievements:

- Creation and entanglement of the largest logic quantum bits to date, showing a code distance of 7, which enables detection and correction of arbitrary errors that occur during the operation of entangled logic gates (the larger the code distance, the greater the resistance to quantum errors). Furthermore, it was shown for the first time that increasing the code distance can indeed reduce the error rate in logic operations.

- Forty-eight small logic quantum bits for executing complex algorithms were implemented, and their performance exceeded that of the same algorithms when executed using physical quantum bits.

- By controlling 280 physical bits, 40 medium-sized error-correcting codes were constructed.

These results herald the arrival of early error-correcting quantum computing and point the way to the development of large-scale logic processors.

Capture neutral atoms and logically fix errors

"Having this many logical quantum bits is a big deal." Mark Saffman of the University of Wisconsin-Madison said, "This is a very impressive achievement for any quantum computing platform." He explained that the new quantum computer's atoms are controlled by light, which benefits it greatly because that control is very efficient.

QuEra's hardware uses neutral atoms, which has several advantages. Quantum information is stored in the nuclear spin of individual atoms, which is relatively stable in terms of maintaining quantum information; and, because each atom of a particular isotope is equivalent, there are no device-to-device differences, as there are with quantum bits based on superconducting hardware; individual atoms can be processed with lasers without the need for wiring, and the atoms can be moved around so that it is possible for any quantum bit to be connected to other quantum bits.

Currently, QuEra's next-generation hardware supports up to 280 atom-based quantum bits. To achieve this, the atoms can be moved between several functional areas: a simple storage area where the quantum bits are stored when they are not being manipulated or measured; there are both logical quantum bits in use and a pool of unused quantum bits that can be mobilized during the execution of an algorithm.

In addition, there is an "entanglement zone", where operations are performed, and a readout zone, where the state of individual quantum bits is measured without interfering with quantum bits elsewhere in the hardware.

Several aspects of neutral atomic quantum bits make it easier to manipulate logical quantum bits. For example, manipulating a logic quantum bit can be as simple as moving all of the atoms that make up the logic quantum bit into the entanglement region and then shining a laser on those atoms to perform the same operation on all of the logic quantum bit's constituent atoms at the same time. A similar operation can be performed on two logical quantum bits by performing a gate operation on them.

In addition, separate measurement regions allow the quantum bit used for error correction to be moved and measured as the algorithm proceeds without disturbing any other component of the logic quantum bit. Furthermore, in some experiments, these quantum bits are kept in memory until the algorithm is complete; at that point, if there is an indication that an error has occurred, they can be measured and the results discarded.

Even the process of initializing logical quantum bits shows its potential benefits. By selecting instances where later measurements showed no signs of error, the fidelity of the initialization reached more than 99.9%, much higher than the success rate of the initialization of a single hardware quantum bit (99.3%).

This time, the team implemented several computer operations, codes and algorithms on the new computer to test the performance of logical quantum bits. They found that while these tests were more preliminary than the calculations that the quantum computer would eventually have to perform, the team has confirmed that the use of logical quantum bits leads to fewer errors than quantum computers that use physical quantum bits.

In one case, they could use a classical computer to estimate the probability of different outcomes for a series of operations; this was then compared to the actual operations. Without any error detection, there is considerable noise in the experimental results. However, as the researchers more rigorously rejected measurements that showed signs of error, the results gradually became clearer: the accuracy of a single measurement rose from 0.16 to 0.62.

But this is not full error correction, says Yuval Boger, QuEra's chief marketing officer: "What happens in the paper is that errors are only corrected once the calculation is complete. Therefore, what we have not yet demonstrated is mid-circuit correction, where we measure ...... during the computation process to correct errors. whether there is a wrong indication, correct the error, and then move on."

In the coming years, thousands of error correcting quantum bits will be deployed

Researchers usually estimate that a fully fault-tolerant or error-free quantum computer would require thousands of logic quantum bits, but Princeton University's Jeff Thompson says it's exciting that some fault-tolerant ideas have been explored in the new experiment. He sees the results as a definite step forward, and with the rapid development of atom-based computers, more progress is bound to be made.

Thompson said, "We are witnessing some defining moments [for atomic computers]."

What's next?

QuEra is a leader in the field of atomic and quantum error correction in neutral Reedsburg. Right now, they have 10,000 atoms (uncorrected) in their system. If they can put all of these atoms to work, they could achieve their goal of 50-600 error-correcting quantum bits in the short term, and then go beyond that with better scaling.

QuEra's approach is to achieve system scaling at a lower cost. Each interconnect costs about $10,000. Reducing these and other systems as the system scales will enable large-scale quantum error-correction systems to be realized at lower cost.

QuEra plans to provide a roadmap for future development in January. Still, we can infer a fair amount of what needs to be accomplished. First, as Borg said, this is not full error correction performed during computation, which QuEra is working to address. In addition, the algorithms used in these tests are not practical, as no commercial customer would pay to run them. Before this can happen, the logic quantum bit count must be increased.

Another reason to increase the number of quantum bits is that, as this work demonstrates, the more quantum bits a logic quantum bit uses, the lower the error rate. If each logical quantum bit requires 10 hardware quantum bits, then the current QuEra hardware can only carry 22 quantum bits at a time.

Obviously, running these demos with 48 quantum bits means that fewer than 10 quantum bits are used, and therefore more errors are uncaught than might occur on a larger machine.

Nonetheless, QuEra points out in its paper that optimized control and enhanced laser power should allow this architecture to reach 10,000 physical bits, so there should be considerable leeway. And, since all control operations are done through the laser, it should be possible to use photonic links to connect independent hardware. Borg also mentioned improving the performance of readout systems by reducing the time it takes for errors to occur.

But the value of all these potential advances rests on the belief that we will eventually be able to perform a series of complex operations on logical quantum bits and correct any errors in real time.

The first half has now moved out of the realm of belief and into the list of proven technologies.