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In a post discussing how it was hardening its protocols to prevent encryption being cracked by powerful quantum computers, Signal noted that although quantum computers already exist, the systems known to exist today do not yet have enough qubits to pose a threat to the public-key cryptography it currently uses.
However, Ehren Kret, chief technology officer of Signal, said: “If a sufficiently powerful quantum computer were built in the future, it could be used to compute a private key from a public key thereby breaking encrypted messages.” This kind of threat is known as Harvest Now, Decrypt Later.
In his post, Kret noted that some experts believe such a quantum computer maybe couple of years away – but he also wrote that the challenges of building a stable quantum computer with sufficient processing power may be insurmountable. “On the high end, some say 30-plus years, and there are even those who assert that we may never solve the challenges necessary to make a quantum computer with enough coherent qubits to break the current public key cryptosystems,” he said.
David Hayes, theory and architecture lead at Quantinuum notes that the entire story of how to build a quantum computer that will produce reliable results rests on the ability to operate quantum error correction codes. “Without these codes, people generally think there will be a hard floor on how low the error rates can be, and the current error rates would severely limit the long-term utility of quantum technology,” he said
When asked about the evolution of quantum technology during a panel discussion at the recent Quantum.tech conference held at Twickenham Stadium, Ilyas Khan, CEO of Quantinuum, discussed his ambition to have in the near future a breakthrough involving entangling two logical qubits, operating below their threshold level of performance to reduce error rates. Entanglement is key to the high level of performance researchers predict will be attained in quantum computing systems. Unlike in a classical, binary computing architecture where the processing power has a linear relationship with the number of binary bits, entanglement offers exponential number-crunching growth as more logical qubits are added.
In theory quantum error correction codes may make it possible to push the error rates down as low as needed, thereby making it possible to run any algorithm. Hayes said that by entangling operations between different logical qubits is a fundamental ingredient of encoding algorithms. “If the technology can’t do an entangling operation between logical qubits, it has no hope of achieving scalable universal quantum computation.”
For some of the presenters at the event, quantum computing is still a long way off. Muni Vinay Kamisetty, vice-president and regional head of engineering at Lazada, an Alibaba subsidiary, said: “Qubits are not stable; quantum capabilities are not up to the mark. Honestly, we don’t have a practical quantum computing use case.”
Another speaker, Clemens Utschig-Utschig, chief technology officer at pharmaceutical company Boehringer Ingelheim, highlighted the extent to which quantum computers need to be developed before they can be used to solve complex molecular chemistry calculations. Since 2021, the company has collaborated with Google Quantum AI, researching and implementing cutting-edge use cases for quantum computing in pharmaceutical research focused on molecular dynamics simulations. He said the research showed over 1,400 logically corrected qubits and that 7.8 billion gates would be needed for calculations based on an important pharma enzyme called P450, which is used to reduce the toxicity of drugs.
Logical qubits are groups of physical qubits working together to perform a computation. For each physical qubit used in a computation, other ancillary qubits perform a range of tasks, such as spotting and correcting errors as they occur. There are some industry estimates that as many as 1,000 or more physical qubits are needed for a logical qubit. Quantinuum's Hayes said the company currently uses 10 physical qubits per logical qubit. There is a big difference, but having a powerful enough quantum computer to tackle the type of problems Utschig-Utschig would like to address is lilely to be a long way off.
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At the moment, classical computers can test if algorithms run on a quantum computing system are giving the expected results. The industry is heading in the direction of delivering what it regards as quantum supremacy. This destination will mean that, due to the complexity of the algorithm, it no longer becomes possible to run it on a classical machine. The time a classical machine would need to take to return an answer would make testing quantum algorithms on such machines no longer practical.
However, the work to achieve supremacy appears disjointed, according to Kamisetty. “Organisations are all working in silos and clusters to achieve quantum supremacy on their own, which decelerates progress,” he said.
Beyond the need for the hardware to develop, there is a sense that quantum computing will involve a return to people in lab coats looking after very fragile pieces of IT infrastructure. In a recent interview with Computer Weekly, Richard Moulds, general manager for Amazon Braket, said: “It’s not like they have racks of servers. These are early stage devices. In some cases you might even describe them as prototype machines. So, they need some care and feeding, and might require calibrating every day. The technology is not mature enough right now, unfortunately, to build quantum computers in an Amazon datacentre.”
There is no reason to believe the industry will achieve quantum supremacy or be able to scale logical qubits to a level where they can solve the type of molecular simulation problems Utschig-Utschig describes. Nevertheless, this hasn’t stopped the industry from preparing for the future possibility that such powerful processing may become available.
“The middle ground seems to be around the five to 10 year time horizon,” said Signal’s Kret. “We are not in a position to judge which timeline is most likely, but we do see a real and growing risk which means we need to take steps today to address the future possibility of a large enough quantum computer being created.”