How big does a quantum computer need to be to accomplish something useful? Physicists from the University of Sussex, UK recently set out to answer this question for two pragmatic computational tasks: breaking the encryption used in Bitcoin transactions and simulating the behaviour of an agriculturally important nitrogen-fixing molecule. By estimating the number of quantum bits, or qubits, that different types of quantum computers would need for each task, members of the team say their theoretical study should help other researchers decide which designs to pursue. Although there is no standard hardware platform for quantum computers, two of the most popular ways of engineering qubits involve superconductors and trapped ions. In either case, the number of qubits available to perform quantum operations is significant, explains Mark Webber, a PhD student at Sussex who is also involved in a Sussex spin-out called Universal Quantum.
In this blog post, our quantum engineer, Luuk Earl, explains the differences between superconducting and trapped-ion qubits and the impact when scaling up quantum computers. For years, quantum computing inched forward, one qubit at a time. Now, the world is waking up to the reality that we need millions of qubits for quantum computers to achieve something truly useful for society. IBM hopes to have 1,000-qubit machines by 2023. Rigetti says it'll do the same in 2024.
While researchers don't understand everything about the quantum world, what they do know is that quantum particles hold immense potential, in particular to hold and process large amounts of information. What is quantum computing and how does it work? Quantum computing exploits the puzzling behavior that scientists have been observing for decades in nature's smallest particles – think atoms, photons or electrons. At this scale, the classical laws of physics ceases to apply, and instead we shift to quantum rules. While researchers don't understand everything about the quantum world, what they do know is that quantum particles hold immense potential, in particular to hold and process large amounts of information. Successfully bringing those particles under control in a quantum computer could trigger an explosion of compute power that would phenomenally advance innovation in many fields that require complex calculations, like drug discovery, climate modelling, financial optimization or logistics. As Bob Sutor, chief quantum exponent at IBM, puts it: "Quantum computing is our way of emulating nature to solve extraordinarily difficult problems and make them tractable," he tells ZDNet. What is a quantum computer?
The usefulness of most quantum computers is still significantly limited by the low number of qubits that hardware can support. But simple fiber optic cables – just like the ones used for broadband connections – could be the answer. A team of researchers from the National Institute of Standards and Technology (NIST) found that, with just a few tweaks, optical fiber can be used to communicate with the qubits sitting inside superconducting quantum computers, with the same level of accuracy as existing methods. Unlike the metal wires currently used, it is easy to multiply the number of fiber optic cables in a single device, which means it is possible to communicate with more qubits. According to NIST, the findings pave the way to packing a million qubits into a quantum computer.
Paul Lipman has worked in cybersecurity for 10 years. Quantum computing is based on quantum mechanics, which governs how nature works at the smallest scales. The smallest classical computing element is a bit, which can be either 0 or 1. The quantum equivalent is a qubit, which can also be 0 or 1 or in what's called a superposition -- any combination of 0 and 1. Performing a calculation on two classical bits (which can be 00, 01, 10 and 11) requires four calculations. A quantum computer can perform calculations on all four states simultaneously.