Optical experiment demonstrates the strong Mpemba effect in a single qubit
Typically, after a physical system is disturbed, it can gradually return toward a state of thermal equilibrium by exchanging heat with its surroundings. Thermal equilibrium is a state in which there is no net transfer of heat between the system and its surroundings.
An optical experiment conducted by researchers at Southeast University demonstrated the strong Mpemba effect in a single qubit, a fundamental unit of quantum information. Typically, a physical system gradually returns to thermal equilibrium by exchanging heat with its surroundings, but under certain conditions, systems that start farther from equilibrium can approach equilibrium faster than those closer to equilibrium. This reverse behavior is known as the Mpemba effect.
The strong Mpemba effect occurs when the initial state of a system has no overlap with the slowest decay mode, causing the relaxation process to be exponentially accelerated. Researchers at Trinity College Dublin and Ludwig-Maximilians University Munich proposed a theoretical model suggesting that multiple modes can share the slowest decay rate, involving the loss of quantum coherence.
To experimentally observe the strong Mpemba effect, the Southeast University researchers simulated a qubit using a single photon, encoding the qubit in the photon's polarization. They prepared the qubit in two distinct starting states: one in an energy eigenstate with no quantum coherence and another in a superposition of two energy states with coherence.
As expected, the qubit in the energy eigenstate approached thermal equilibrium faster than the one in superposition, even though the former had a higher nonequilibrium free energy and was initially farther from equilibrium.
The study, published in Physical Review Letters, provides new insights into how the strong Mpemba effect could influence a system's journey back to equilibrium. The researchers also showed that removing quantum coherence accelerates relaxation, while coherence carries additional nonequilibrium free energy beyond classical populations. This research could contribute to the understanding of the strong Mpemba effect and potentially inform the development of new quantum thermal machines that leverage this phenomenon.
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