Resolving vacuum fluctuations in an electrical circuit by measuring the Lamb shift

Area of Science:

• Quantum physics
• Solid-state systems
• Superconducting circuits

Background:

• Quantum theory posits that vacuum is not empty but filled with virtual particles.
• The Lamb shift, a quantum electrodynamics effect, arises from virtual photon interactions with charged particles.
• Observing the Lamb shift in solid-state systems is crucial for understanding quantum phenomena in macroscopic systems.

Purpose of the Study:

• To experimentally demonstrate and measure the Lamb shift in a solid-state system.
• To investigate the strong coupling between a superconducting qubit and the quantum vacuum field.
• To explore the influence of vacuum fluctuations on qubit properties.

Main Methods:

• Utilizing a superconducting circuit as a quantum bit (qubit) coupled to a transmission-line resonator.
• Measuring the Lamb shift by analyzing changes in the qubit transition frequency.
• Investigating the qubit's vacuum field coupling strength relative to single-photon coupling.

Main Results:

• Measurable Lamb shifts of up to 1.4% of the qubit transition frequency were observed.
• The superconducting qubit exhibited stronger coupling to the vacuum field than to a single cavity photon.
• The observed effects were explained by considering the anharmonicity of higher qubit energy states.

Conclusions:

• The Lamb shift is experimentally observable in solid-state superconducting circuits.
• Quantum vacuum fluctuations play a significant role in the behavior of superconducting qubits.
• This work provides a novel platform for studying fundamental quantum electrodynamics in solid-state devices.