When people first hear about quantum computing, a frequent question is “what is the point in trying to build such a quantum computer?”. The answer to this very important question lies, as the name suggests, in the definition of the term “quantum advantage”. Loosely speaking, this term refers to any type of advantage that a quantum computer could bring.
Areas where a quantum computer may have an advantage over a classical one:
- Computational efficiency: By taking advantage of phenomena unique to the quantum world such as quantum entanglement and quantum superposition, quantum algorithms have the potential to solve certain problems using significantly less computational steps than a classical algorithm. An example of this is Shor’s algorithm which is an algorithm for factoring numbers – an incredibly hard task for a classical computer (at least for large enough numbers). The quantum algorithm reduces the complexity of the computation exponentially: a classical computer will factor an integer made of a small number of digits faster than a quantum computer, but for very big integers, the quantum computer will be (much) faster. The question of how big these “very big integers” need to be to see an improvement is not yet settled. An experiment that may enable to reach a computational quantum advantage more quickly is boson sampling. Indeed, boson sampling is a sampling task which can be performed on a relatively small quantum device and runs exponentially faster than when it is performed on a classical device. This is already being realised on a small scale on photonic hardware such as the one Quandela offers. As of today, there is no known useful application that inherits the quantum advantage of boson sampling but looking for such algorithms is a promising research area, which Quandela is heavily contributing to.
- Computational accuracy: When you solve a problem or run a simulation on a classical computer, you are almost certainly using numerical methods to approximate the solution to your problem. Once a large-scale quantum computer is available, one could solve problems more accurately or reach the required accuracy of a solution more quickly. A great example of where this is promising is in simulating large molecules. You can read more about that here.
- Cost/Energy efficiency: One of the main issues of today’s classical computers is the large energy consumption of large computing centres, for instance those necessary for ChatGPT. Energy consumption is a potential area of Quantum Advantage. As an example, today’s high-performance computing centres consume around 20 MW, whereas Quandela’s largest computer is projected to consume below 1MW, reas our article on the subject here. In particular, Quandela’s approach has relatively low requirements for cryogenics compared to most other technologies envisioned for quantum computing.
Frequently asked questions
- Has quantum advantage been achieved yet? As of today, there have been several experiments claiming a quantum advantage in areas such as generative learning, optimisation, and sampling tasks. The slightly bizarre nature of the quantum world also enables the generation of true randomness which is not possible on a classical computer and while these breakthroughs are still slightly artificial and far from any real-world applications, they demonstrate nonetheless the promising future of quantum computing.
- How can we reach a Quantum Advantage? A quantum advantage may be reached in the near term, for instance using boson sampling. However, to reach the full capabilities of quantum computers, one will probably need to implement error mitigation and error correction to fight against the errors that occur.
- Does Quantum Advantage mean the end of classical computers? No, quantum computers are not expected to replace classical computers at any point. Classical computers will still be used for most computations with only a few specialised tasks being done on a quantum computer via a cloud. Moreover, quantum computers can be used in conjunction with a classical computer. Already today there exist hybrid algorithms called variational quantum algorithms which take advantage of the strengths of both quantum and classical computers.