Quantum Energy Teleportation for Instantaneous Extraction of Energy from a Finite-Temperature Heat Bath

A quantum system at a finite temperature possesses thermal energy. However, extracting that energy to the outside usually requires a certain amount of time. As shown in Figure 1, by preparing an object at a lower temperature and bringing it into contact with the quantum system, a heat flow is generated, and thermal energy is released to the outside. This is because the generation of that heat flow requires global time evolution within the quantum system, necessitating a wait for a typical time determined by the system's dynamics.

One might think that if an external object at a very low temperature could be prepared, it would be possible to extract thermal energy by bringing it into contact with the finite-temperature quantum system, even if only for an instant. However, for a quantum system at or below a certain temperature, this produces the opposite effect.

As shown in Figures 2 and 3, an external object at a lower temperature (represented by a hand in the figure) is brought into instantaneous contact with subsystem B of a quantum system that is at or below a certain threshold temperature.

The contact in Figure 3 is only for an instant, after which the object is immediately separated from B. Naively, one might expect that if the temperature of the external object is sufficiently low, thermal energy would have transferred to the external object. But the reality is the opposite; this operation actually increases the energy of B and, consequently, the energy of the entire finite-temperature quantum system. This phenomenon is called "Strong Local Passivity" (SLP). This concept of SLP is a phenomenon that my collaborators and I theoretically discovered in 2014.

The reason this strong local passivity appears in the temperature range below the threshold temperature is that the contact between B and the external object is too rapid. If one were to touch B slowly and gently, thermal energy would indeed move from B to the external object, but if the object pokes B quickly and impatiently, the rapid motion of the external object further excites B itself. Therefore, the external object does not extract energy from the thermal quantum system, but rather injects energy into it.

However, there is a way. By using a protocol I first proposed in 2008 called "Quantum Energy Teleportation," it is possible to extract thermal energy from subsystem B of this finite-temperature quantum system, which is at a temperature below that threshold, almost instantaneously.

The experiment on quantum energy teleportation that broke this strong local passivity was actually conducted at a research institute in Canada in 2023, proving that our theory is correct. In a time scale much shorter than that required to extract the original thermal energy to the outside, we were able to extract not only the thermal energy but also the energy of the quantum fluctuations of the quantum system (zero-point energy) to the outside.

This is a story that can also be applied to general finite-temperature systems. For example, as shown in Figure 4, in a quantum system in a finite-temperature thermal equilibrium state, by measuring another subsystem A and then performing a physical operation on B that depends on the measurement result, energy can be extracted from B to the outside in an extremely short time.

This means that quantum energy teleportation can be used to rapidly cool a subsystem locally. In general, quantum devices such as quantum computers dislike thermal fluctuations that destroy quantum coherence. If one wishes to perform high-precision quantum calculations at B, it becomes possible to discard the thermal fluctuations and thermal energy of B to the outside using quantum energy teleportation.

In this way, quantum energy teleportation also provides an important mechanism that can be applied to the development of future quantum integrated circuits (quantum ICs).

It has also been introduced in Quanta Magazine, published by the Simons Foundation.

Biggest Breakthroughs in Physics: 2023