The Toronto-based company Xanadu claims that their quantum device, dubbed Borealis, took only 36 microseconds to solve a mathematical problem that would have required over 9000 years of computation on today’s most powerful supercomputers.
In a recently published paper in the research journal Nature, Xanadu described this achievement as a demonstration of quantum advantage. Quantum advantage is a term that is often used when a quantum computer demonstrates an ability to efficiently complete computational tasks that classical supercomputers would not be able to perform within a feasible time frame. In this case, the task was a mathematical problem called Gaussian boson sampling (“GBS”), which is commonly used as a benchmark for evaluating the performance of quantum computers.
The enormous differences in computational performance between classical and quantum computers are due to the unique properties of quantum physics. In classical computing, data is processed sequentially in a linear fashion using binary bits, which each store values of either 0 or 1. In contrast, quantum computers can process data in parallel by exploiting the principle of quantum superposition, which posits that a quantum particle can exist in multiple states at any given time. As such, the qubits used in quantum computing can have a value of both 0 and 1 simultaneously, allowing for more data to be processed at once.
Borealis’ Photonics-Based Design Has Several Advantages over Other Approaches
Multiple approaches to quantum computing, championed by just as many players, are currently being investigated. For example, Google’s Sycamore device, which demonstrated quantum advantage in 2019, used superconducting metal circuits to form its 53 qubits. IBM also pursued a similar superconductor-based approach and unveiled its 127-qubit Eagle device in 2021.
As an alternative to using superconductors, there also exists a photonics-based approach to quantum computing which involves using photons (particles of lights) to act as qubits. Rather than relying on superconductors to serve as qubits, photonics-based quantum computers use networks of fibre optic cables and beam splitters to manipulate pulses of light in a way that causes the photons to exhibit quantum properties and behave as qubits. This idea was proven to be feasible in 2020 when a team of researchers from the University of Science and Technology of China became the first to achieve quantum advantage using their photonics-based Jiuzhang device.
One of the main advantages of photonics-based devices such as Jiuzhang and Borealis is that they can be operated at room temperatures. In contrast, the superconducting circuits in Sycamore and Eagle need to be cryogenically cooled to temperatures near absolute zero in order for them to function efficiently.
Furthermore, when compared to earlier photonics-based devices like Jiuzhang, Borealis also has a massive advantage in that it is programmable. While Jiuzhang’s design only allows it to perform a single type of calculation, Borealis features programmable beam splitters that allow the device to be reconfigured to perform a variety of different tasks. Xanadu has even made Borealis publically available through Xanadu Cloud and Amazon Bracket, where researchers and members of the public can design and submit their own workloads for Borealis to compute.
However, while Borealis showcases many impressive innovations, experts believe that a commercially relevant quantum computer would need to boast at least one million qubits in order to support practical real-world applications. Specifically, a large number of qubits will be required in order to have enough computational resources to correct errors which are prevalent in all quantum systems.
Nonetheless, in demonstrating quantum advantage, operability at room temperature, and programmability, the researchers at Xanadu are confident that Borealis represents “a critical milestone on the path to a practical quantum computer.”
References: 1. Lars S Madsen et al, “Quantum Computational Advantage with a Programmable Photonic Processor” (2022) 606 Nature 75.
2. Han-Sen Zhong et al, “Quantum Computational Advantage Using Photons” (2020) 370:6523 Science 1460.
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