John Clarke, Michel H. Devoret, and John M. Martinis received the Nobel Prize in Physics 2025 for conducting a series of experiments to demonstrate that the effect of quantum tunneling on a microscopic scale, used to be viewed as only happening in microscopes, can be made concrete in a macroscopic system big enough to be held in the hand [1].

So what is quantum tunneling? Quantum tunneling is an effect under quantum mechanics that describes properties that are significant on a scale involving single particles. Consequently, quantum tunneling used to be considered only happening in the microscopic scale, which is much smaller than what can be observed using the optical microscope. If we put the quantum tunneling effect on a macroscopic scale, which we can perceive, it is pretty bizarre and counterintuitive (as the graph below shows) [2]. According to common sense, the ball should bounce back when you throw it towards the wall. However, in the world of quantum mechanics, the ball, precisely some proportion of the ball, would directly pass through the wall and suddenly appear on the other side. In the past, this was considered to only happen on a microscopic scale.[2]

After 56 years, Leonid Mandelstam and Mikhail Leontovich’s early ideas on quantum tunneling were realized on a macroscopic scale in experiments by John Clarke, Michel H. Devoret, and John M. Martinis. Using superconducting circuits—where current can flow without resistance—they observed that the system, initially in a zero-voltage state, could escape this state through quantum tunneling. This transition was detected as the sudden appearance of a voltage, demonstrating quantum behavior in a macroscopic system [1]. These superconducting circuits can also possess discrete energy levels, forming the basis for quantum bits (qubits) in modern quantum technology and quantum computing, and are described by the Josephson effect.

Superconducting circuits based on Josephson junctions not only exhibit macroscopic quantum tunneling but can also be engineered as “artificial atoms” with discrete energy levels. By defining two quantum states, |0⟩ and |1⟩, from these levels, researchers create quantum bits (qubits). Unlike classical bits that are either 0 or 1, qubits can exist in a superposition of both states simultaneously. Moreover, multiple qubits can be entangled, which is known as quantum entanglement, enabling massively parallel computation and complex correlations within an extremely small amount of time. These properties allow quantum computers to potentially outperform classical ones in specific tasks such as integer factorization, quantum simulation, and optimization.

[3]

A refrigerator festooned with microwave cables cools Google’s quantum chip nearly to absolute zero.

With advances in experimental techniques, a major milestone known as quantum supremacy was demonstrated in 2019 by John Martinis’s Google team. Their processor with 53 qubits takes about 200 seconds to sample one instance of a quantum circuit a million times—the benchmarks currently indicate that the equivalent task for a state-of-the-art classical supercomputer would take approximately 10,000 years [4]. This dramatic increase in speed compared to all known classical algorithms is an experimental realization of quantum supremacy for not only this specific computational task, heralding a much-anticipated computing paradigm, but also implies the further developmental potential of quantum computing.

Reference

[1] “Nobel Prize in Physics 2025.” NobelPrize.Org, www.nobelprize.org/prizes/physics/2025/press-release/. Accessed 10 Oct. 2025. 

[2] Schirber, Michael. “Nobel Prize: Quantum Tunneling on a Large Scale (Updated).” Physics, American Physical Society, 7 Oct. 2025, physics.aps.org/articles/v18/170. 

[3] Quantum Computers Take Key Step toward Curbing Errors | Science | AAAS, www.science.org/content/article/quantum-computers-take-key-step-toward-curbing-errors. Accessed 24 Oct. 2025. 

[4] Arute, Frank, et al. “Quantum supremacy using a programmable superconducting processor.” Nature, vol. 574, no. 7779, 23 Oct. 2019, pp. 505–510, https://doi.org/10.1038/s41586-019-1666-5.