Manipulating the quantum state of an electrical circuit

Area of Science:

• Quantum computing
• Solid-state physics
• Superconducting circuits

Background:

• Superconducting circuits are promising candidates for quantum computing.
• Controlling and measuring quantum states in solid-state systems remains a challenge.

Purpose of the Study:

• To design and operate a superconducting circuit behaving as a two-level quantum system.
• To demonstrate programmable quantum state evolution and projective measurement.
• To assess the potential for solid-state quantum processors.

Main Methods:

• Designed and operated a superconducting tunnel junction circuit, termed the "quantronium."
• Utilized microwave pulses for arbitrary quantum state evolution programming.
• Employed a pulsed readout subcircuit for projective state measurement.

Main Results:

• The "quantronium" circuit successfully emulated a two-level atom.
• Programmable control and measurement of quantum states were achieved.
• A high quantum coherence quality factor (Qphi ≈ 25,000) was measured.

Conclusions:

• The "quantronium" circuit demonstrates high quantum coherence.
• This circuit design is a viable building block for future solid-state quantum processors.