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A new trick brings stability to quantum operations

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A new trick brings stability to quantum operations

Author: Oliver Morsch (freelance author for ETH Zurich) Date: April 8, 2026 Source: https://ethz.ch/en/news-and-events/eth-news/news/2026/04/a-new-trick-brings-stability-to-quantum-operations.html Paper: Kiefer Y, Zhu Z, Fischer L, Jele S, Gächter M, Bisson G, Viebahn K, Esslinger T: Protected quantum gates using qubit doublons in dynamical optical lattices. Nature, 8 April 2026, DOI: 10.1038/s41586-026-10285-1

Summary

ETH Zurich researchers led by Tilman Esslinger built a swap gate for neutral-atom qubits using geometric (Berry) phases. The gate is inherently robust against experimental noise because geometric phases depend on the topology of the rotation path, not on timing, speed, or laser intensity.

Setup

  • Extremely cold potassium atoms trapped in optical lattices (artificial crystals of light)
  • Laser beams bring atom pairs close enough that wavefunctions overlap
  • Potassium atoms are fermions → Pauli exclusion prevents identical quantum states → geometric phase naturally emerges
  • The phase depends on the path geometry, not the dynamics → robust against laser intensity fluctuations and speed variations

Results

  • 99.91% fidelity on state exchange (swap gate)
  • Applied simultaneously to 17,000 qubit pairs
  • Sub-millisecond operation time
  • Noise-resilient: "Independent of the speed with which we manipulate the atoms, or how strongly the laser intensity fluctuates"

Limitations and next steps

  • Swap gates alone are insufficient for universal quantum computation
  • Team has demonstrated "half-swap" gates incorporating atomic collisions to create entanglement
  • Integration with quantum gas microscopes planned for selective individual qubit pair manipulation
  • Need to scale from bulk parallel operations to individually addressable operations

Key quotes

  • "the tunnel effect depends very strongly on the intensity of the laser light" (on why previous approaches were fragile)
  • "Independent of the speed with which we manipulate the atoms, or how strongly the laser intensity fluctuates" (on why geometric phases are robust)