The effort to build truly useful quantum computers often comes down to making them bigger by adding qubits, the quantum bits that are the basic building blocks of these devices. But creating quantum chaos inside them could have the same effect 鈥� and let quantum computers perform some tasks that seem too big for them to handle.
Creating true quantum randomness 鈥� which is distinct from quantum chaos, and can be a useful resource in quantum technologies 鈥� usually requires a lot of engineering. But at the California Institute of Technology and his colleagues have discovered how to leverage chaos to do it for us.
鈥淭hey found a very efficient way of effectively translating classical randomness, which is something we understand very well, which is very easy to generate, into quantum randomness, which is something that鈥檚 hard to understand and also much harder to generate,鈥� says at Max Planck Institute for the Physics of Complex Systems in Germany.
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Quantum randomness means a complete lack of patterns and predictability. In a truly random system, there is no way to predict the properties of a quantum object even if you have interacted with it before. Because quantum physics allows for more correlations than exist for non-quantum objects, quantum and classical randomness are also not equivalent 鈥� and the classical kind is much easier to create. Chaos, on the other hand, can be more predictable, but chaotic systems are extremely sensitive to their conditions, so even slight changes in the environment can change a chaotic object鈥檚 behaviour.
The researchers analysed how the quantum version of this sensitivity may help quantum objects become more random. They simulated a chaotic system that was made up of many qubits. In their set-up, making measurements on some qubits pushed others into random quantum states and the researchers could quantify the amount of quantum randomness in that final state.
They ran many simulations to determine the initial properties that would result in the system gaining the most quantum randomness after being allowed some time to experience chaos. Ultimately, making the qubits鈥� initial state more classically random turned out to be the best choice. Mok says the team was surprised to find that this conversion turned each unit, or bit, of classical randomness into as much quantum randomness as if they had added a whole extra qubit to the system. He says his team found a shortcut.
Mok says it may already be possible to concretely test this result because some experiments with extremely cold atoms have previously created chaotic systems like the one his team studied. The next step is to use similar experiments to confirm that a mix of classical randomness and quantum chaos can indeed be helpful for tasks such as benchmarking the atoms鈥� ability to work as qubits or a process called 鈥渟hadow tomography鈥�, which is used to examine qubits鈥� quantum states, both of which require quantum randomness.
Journal reference: Physical Review Letters,
