Hawking Radiation

Quantum simulation of Hawking radiation and curved spacetime with a superconducting on-chip black hole

Hawking radiation is one of the quantum features of a black hole that can be understood as a quantum tunneling across the event horizon of the black hole, but it is quite difficult to directly observe the Hawking radiation of an astrophysical black hole.

In the classical picture, a particle falls into a black hole horizon and the horizon prevents the particle from turning back, then escape becomes impossible. However, taking into account quantum effects, the particle inside the black hole is doomed to gradually escape to the outside, leading to the Hawking radiation.

The problem is that direct observation of such a quantum effect of a real black hole is difficult in astrophysics. For a black hole with solar mass, the associated Hawking temperature is only ~10−8 K and the corresponding radiation probability is astronomically small. Given by this, various analog systems were proposed to simulate a black hole and its physical effects in laboratories.

Over the past years, the theory of Hawking radiation has been tested in experiments based on various platforms engineered with analog black holes, such as using shallow water waves Bose-Einstein condensates (BEC) optical metamaterials and light, etc.

On the other hand, the developments of superconducting processors enable us to simulate various intriguing problems of many-body systems, molecules, and to achieve quantum computational supremacy.

However, constructing an analog black hole on a superconducting chip is still a challenge, which requires wide-range tunable and site-dependent couplings between qubits to realize the curved spacetime.

Coincidentally, a recent architectural breakthrough of tunable couplers for superconducting circuit which has been exploited to implement fast and high-fidelity two-qubit gates offers an opportunity to achieve specific coupling distribution analogous to the curved spacetime. We develop such a superconducting processor integrated with a one-dimensional (1D) array of 10 qubits with interaction couplings controlled by 9 tunable couplers, which can realize both flat and curved spacetime backgrounds.

The quantum walks of quasi-particle excitations of superconducting qubits are performed to simulate the dynamics of particles in a black hole background, including dynamics of an entangled pair inside the horizon. By using multi-qubit state tomography, Hawking radiation is measured which is in agreement with theoretical prediction. This new constructed analog black hole then facilitates further investigations of other related problems of the black hole.

Observation of analog Hawking radiation

Black holes emit thermal radiation leading to evaporation, known as Hawking radiation. However, its observation is a challenge even for an analog black hole due to the accuracy of the experiment. The Hawking radiation of a black hole is spontaneous in nature. The first realization of spontaneous Hawking radiation in an analog experiment was in BEC system. Here we report an observation of analog Hawking radiation on the superconducting quantum chip, which is also the first quantum realization of “lattice black hole” originally proposed by T. Jacobson more than twenty years ago.

Hawking predicted that the entanglement entropy increases when a black hole forms and evaporates due to the Hawking radiation. Each Hawking particle is entangled with a partner particle in the black hole. Such kind of quantum feature plays a crucial role in studying black holes and quantum information.