StarTalk Radio

Macroscopic Quantum Tunneling with John Martinis

January 6, 2026

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  • The Nobel Prize in Physics for 2025 was awarded to John Martinis and Michel Devere for the discovery of macroscopic quantum mechanical tunneling and energy quantization in an electric circuit. 
  • Macroscopic quantum tunneling in circuits, unlike superconductivity which is a geometric buildup of microscopic quantum effects, involves observing quantum mechanics in electrical variables like current and voltage on a dime-sized chip. 
  • The development of quantum computers, which utilize qubits existing in a definite state of both zero and one simultaneously, is heavily reliant on the physics of macroscopic quantum phenomena like those observed in Josephson junctions. 

Segments

Nobel Prize and Macroscopic Tunneling
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(00:01:17)
  • Key Takeaway: John Martinis was awarded the 2025 Nobel Prize in Physics for demonstrating quantum mechanics in macroscopic electrical circuits.
  • Summary: The discovery involved observing that the current and voltages in an electrical circuit, about the size of a dime, obey quantum mechanics. This is distinct from superconductivity, where macroscopic effects arise from the geometry of repeating microscopic quantum mechanics. The work confirmed predictions regarding macroscopic quantum tunneling in electrical systems.
Tunneling Mechanism Explained
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(00:10:10)
  • Key Takeaway: Quantum tunneling in this context is observed as a system transitions across an energy barrier between a zero-voltage superconducting state and a resistive state, governed by Josephson equations.
  • Summary: Tunneling occurs when a particle overcomes an energy barrier without sufficient energy, which in this circuit involves the transition from superconductivity to a normal resistive state. This transition is associated with a potential barrier that the system tunnels through. The time taken for tunneling is not instantaneous, contrary to some common assumptions, but is measurable via the ’tunneling traversal time’ effect.
Practical Applications of Quantum Circuits
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(00:13:06)
  • Key Takeaway: The ability to engineer circuits obeying quantum mechanics creates a new ‘periodic table’ of quantum devices, paving the way for practical quantum computers.
  • Summary: This discovery allows for the creation of new quantum devices using components like inductors, capacitors, and Josephson junctions, expanding beyond traditional chemistry-based material design. This foundation is crucial for building quantum computers using existing electronic technology infrastructure. The Nobel recognition came decades after the initial 1985 theoretical work, reflecting the time needed to see its full technological impact.
Qubit Definition and Quantum Computing Power
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(00:30:31)
  • Key Takeaway: A qubit is a quantum bit that exists in a definite state of both zero and one simultaneously, enabling massive parallel computation.
  • Summary: Unlike classical bits, a qubit’s state is not merely probabilistic but a definite superposition of states, analogous to an electron’s cloud distribution around a nucleus. With $N$ qubits, $2^N$ calculations can be performed in parallel, meaning 53 qubits can handle $10^{16}$ parallel states. This power is essential for algorithms like Shor’s algorithm, which threatens current RSA encryption.
Quantum Computing and AI Synergy
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(00:49:34)
  • Key Takeaway: Quantum computing is expected to function as a coprocessor to supercomputers, accelerating AI applications, especially those involving quantum mechanical simulations.
  • Summary: The future likely involves quantum computers aiding classical supercomputers, particularly for problems involving quantum mechanics, such as molecular modeling. This synergy could lead to quantum-aided results for consumer queries within the next decade. The complexity of simulating the human brain is cited as a potential application for this combined computational power.