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Will 2025 mark the beginning of practically useful quantum computers?
A major impediment facing quantum computing was that of scalability, the ability to significantly increase the number of qubits in a quantum computer. This has been particularly difficult in light of error correction, which has been a problem pretty much since the genesis of quantum computers. There have been several attempts to address the issue, but none of them panned out. In 2024, however, some developments have shown real promise. In particular, in a paper recently published in Nature, Google has claimed that it has been able to surmount this obstacle using its “Willow” quantum processor, thereby paving the way for large-scale quantum computers to become a practical reality in the near future.
The problem of error correction and scalability
Unlike classical computers, which use bits as carriers of information, quantum computers use qubits for the same purpose. These qubits are particles such as photons (particles of light), electrons, etc. Since these are microscopic particles, they exhibit quantum behaviour and are incredibly susceptible to the external environment. The slightest disturbance due to temperature fluctuations or electromagnetic fields can cause the information contained by them to start decaying, a phenomenon known as quantum decoherence or “noise,” which is the primary obstacle in building quantum computers.
The maximum number of physical qubits in a quantum processing chip is a little over 1,000, a feat which has been achieved by both IBM and Atom Computing, a California-based startup.
While it is impossible to completely remove noise from the system, the objective is to limit it to the extent of providing sufficient time for computation. This is called quantum error correction. Due to noise, the physical qubits comprising the quantum computer get eaten up by the system, which then drastically reduces the number of functional or “logical” qubits - the ones which are capable of performing computations. So, for instance, the maximum number of physical qubits in a quantum processing chip is a little over 1,000, a feat which has been achieved by both IBM and Atom Computing, a California-based startup. However, these have limited practical utility due to a lack of error correction.
Up until recently, quantum error correction has been notoriously difficult to achieve. However, without it, it is impossible to build large-scale quantum computers, which is why there has been a shift in the industry towards error correction and scalability rather than simply increasing the number of physical qubits in the system.
The Willow chip and Google’s assertions
While Google had staked its claim for achieving “quantum supremacy” as far back as 2019 with the announcement of its 54-qubit Sycamore processor, it did not make much headway subsequently. On December 9, 2024, it announced its 105-qubit Willow quantum processor with the claim that it could perform a standard benchmark computation in under five minutes, a task which would take the second-fastest supercomputer in the world, Frontier, about 10 septillion (1025) years to accomplish. Though this may seem like a major accomplishment, the fact is that this is true for a benchmark computation called Radar Cross Section (RCS) and has virtually no practical utility.
The team at Google’s Quantum AI has shown with Willow that as the qubits were made larger, they made half as many errors as the physical qubits comprising them.
What was much more interesting, however, was the assertion that Willow’s error correction increases exponentially as its qubits are scaled up. The team at Google’s Quantum AI has shown with Willow that as the qubits were made larger, they made half as many errors as the physical qubits comprising them. If this increase is sustainable, it will pave the way for more large-scale quantum computers which get better at computation as the number of qubits increases, an unprecedented achievement.
Other key attempts at achieving scalability
In November 2024, Microsoft and Atom Computing were able to demonstrate a computation using 24 logical qubits using neutral atoms, the highest number to date. To put this into perspective, as per Microsoft’s Logical Qubit Roadmap, reaching 100 logical qubits will provide a scientific advantage by solving scientific problems, which classical computers are incapable of. Subsequently, reaching 1000 logical qubits will provide an industrial advantage by enabling the discovery of novel material compounds.
Along with the release of its Condor processor, IBM had also announced its decision to shift more towards error correction and scalability. In November 2024, it provided the world’s first demonstration of two quantum processing units (QPUs) working in tandem to execute a circuit beyond the capabilities of each processor. This is part of IBM’s broader goal of “modular quantum computing,” wherein multiple QPUs will work in concert and provide scalable quantum computers.
The lack of efficient quantum error correction has been the chief culprit behind this since the utility of quantum computers is limited primarily by a lack of scalability.
What it means for the future of quantum computers
The biggest hurdle for quantum computing till date, particularly from an investment point-of-view, has been the lack of its practical utility and applications. The absence of any tangible results detracts investors since they have no guarantee for returns on their investment. The lack of efficient quantum error correction has been the chief culprit behind this since the utility of quantum computers is limited primarily by a lack of scalability.
For quantum computing, 2024 witnessed a sharp shift towards enhanced error correction and scalable quantum computers. This may provide the impetus for private investment in the field, which, up until now, has largely been driven by government investment, particularly in Global South nations like India, which do not have Big Tech firms like IBM and Microsoft. The landscape of quantum computing is steadily shifting, and 2025 may turn out to be the breakthrough year the technology has been striving towards. The recent announcement of four Thematic Hubs under India’s National Quantum Mission is an excellent starting point for the country to establish its foundation in quantum technology. The practical utility of quantum computers will bring in the much-required investment from private players and startups, which is sorely needed to spur innovation in the field.
Prateek Tripathi is a Research Assistant at the Observer Research Foundation.
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