Long-Lasting Quantum Coherence Observed: New Discovery Could Help Overcome Key Obstacle In Creation Of Quantum Computers

The world of subatomic particles, governed by the laws of quantum mechanics, is one that would appear extremely weird to us denizens of a macroscopic world. In the quantum realm, at least insofar as we can understand, particles are in a state of superposition, wherein they exist in two or more states simultaneously — a cat that is both dead and alive, so to speak.

However, this “coherence” lasts for only a fraction of a second before the whole system decoheres — a phenomenon that marks the transition from the realm of quantum to classical mechanics.

The fact that a coherent quantum state is short-lived is what allows reality as we know it to exist, but, for researchers looking to exploit superposition to create quantum computers, this presents a major roadblock. For these researchers, looking for ways to prevent, or at least delay decoherence — thereby preserving the state of superposition that makes quantum computers so much faster than their conventional counterparts — is a key goal.

Now, in a paper published Friday in Physical Review Letters, a team of researchers described the observation of a natural mechanism under which such resilience to decoherence spontaneously emerges in a quantum system.

“Quantum properties can be exploited for disruptive technologies but are typically very fragile,” co-author Gerardo Adesso from the University of Nottingham, told Phys.org. “Here we report an experiment which shows for the first time that quantum coherence in a large ensemble of nuclear spins can be naturally preserved under exposure to strong dephasing noise at room temperature, without external control, and for timescales as long as a second and beyond.”

This discovery was made in a two and four qubit system, where such “freezing” was automatically seen if the initial quantum states were optimal. Moreover, this resilience to decoherence seems universal, making it especially useful for researchers working on quantum technologies.

“The universality paves the way toward designing a novel generation of quantum-enhanced devices able to harness coherence for unscathed performance in realistic and adverse conditions,” Adesso told Phys.org.