A new universal method can solve quantum problems crucial to future computing

We are inching closer to a quantum world.
Rupendra Brahambhatt

Quantum computers are advanced machines capable of performing complex tasks and calculations by employing the laws of quantum mechanics. They have applications in research related to artificial intelligence, drug manufacturing, climate change, cybersecurity, and various other fields. A study recently published in the journal Nature reveals a set of computational operations that could make quantum computers more accurate than ever.

Since quantum computers solve problems that are even too complex for supercomputers (classical computers), they have to deal with enormous amounts of data, which makes them more susceptible to error-causing disturbances. However, a single error from such computers can lead to the loss of large amounts of valuable information. Therefore, engineers and scientists provide quantum computers with strong error-correction mechanisms to avoid any discrepancies.

A team of researchers from Germany’s University of Innsbruck, RWTH Aachen University, and Forschungszentrum Jülich research institute has proposed a method that could lead to the rise of error-free quantum computers.  is an overview of their research.

A universal set to program all algorithms

A new universal method can solve quantum problems crucial to future computing
Artist impression of gate operations on logical quantum bits. Source: Johannes Knünz

You can imagine the capabilities of a quantum computer from the fact that it is believed to be about 158 million times faster than the most powerful supercomputer on Earth. A complex task that can take thousands of years to get done using a classical computer, can be completed within a couple of minutes by a quantum computer. However, there are various challenges that we need to overcome before quantum computing becomes a mainstream technology.

A conventional computer avoids errors by making redundant copies of information in the form of bits. The copies are further used to verify the data. However, the laws of quantum mechanics do not permit data copying from one qubit to another. So in the case of quantum computers, instead of copying, scientists distribute data into numerous physical qubits for achieving information redundancy to solve problems.  

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Researchers in Germany have come up with a computational operation that involves two logical quantum bits and can be employed for any kind of task. The mentioned operation is actually represented by a set of universal gates or quantum circuits capable of processing all types of mathematical information. Physicist Lukas Postler, one of the authors of the study, claims that the universal set can be used in a quantum computer to program all algorithms.

"In this work we demonstrated the implementation of a fault-tolerant universal gate set, where it is ensured that a single error on a physical qubit can not lead to an error in the encoded logical quantum information. A universal set of gates is necessary to approximate any operation possible on a quantum computer (this holds true for error-corrected qubits as in our case but also for calculations on bare physical qubits)," he told Interesting Engineering.

During the study, the universal set was applied on an ion-trap quantum computer, a machine that processes quantum information through the motion of charged atomic particles suspended in free space under the influence of an electromagnetic field. The ion trap computer contained 16 atoms in total. 

The two logical bits of the set called CNOT gate and T gate stored quantum information. Each bit was spanned over seven atoms and for the first time, scientists were able to implement a universal gate on fault-tolerant bits. Fault tolerance is the ability of a system to continue its operations even after the failure of some of its units.

“T gates are very fundamental operations,” they are particularly interesting because quantum algorithms without T gates can be simulated relatively easily on classical computers, negating any possible speed-up. This is no longer possible for algorithms with T gates,”  author Markus Müller said, explaining the significance of T gate.

The error-free approach delivers accuracy, but is slightly more complicated

Quantum information stored in logical quantum bits requires computational operations to get processed, however, such operations are likely to cause errors. Therefore, it's considered complicated to implement universal gates on fault-tolerant logical bits.

“The fault-tolerant implementation requires more operations than non-fault-tolerant operations. This will introduce more errors on the scale of single atoms, but nevertheless the experimental operations on the logical qubits are better than non-fault-tolerant logical operations.” co-lead researcher Thomas Monz explained.

Monz further confirms that although the implementation of a universal gate set makes the processing part more complex, it delivers better and more accurate results. Scientists now plan to test this error-free approach on larger and more powerful quantum machines.

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