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Decoherence in Josephson qubits from dielectric loss.
John M Martinis1, K B Cooper, R McDermott
1Department of Physics, University of California, Santa Barbara, California 93106, USA.
Physical Review Letters
|December 31, 2005
Summary
Dielectric loss from two-level states significantly limits superconducting qubit performance. Reducing this loss with improved materials and smaller junctions enhances coherence times, enabling complex quantum operations.
Area of Science:
- Quantum computing
- Superconducting quantum bits (qubits)
- Materials science
Background:
- Dielectric loss is a primary cause of decoherence in superconducting qubits.
- This loss, stemming from insulating materials or tunnel junctions, limits qubit coherence times.
- Two-level defects are identified as a key source of resonant dielectric loss.
Purpose of the Study:
- To identify and quantify the dominant decoherence sources in superconducting qubits.
- To demonstrate that dielectric loss from two-level defects is a major contributor to short coherence times.
- To investigate methods for reducing dielectric loss and improving qubit performance.
Main Methods:
- Analysis of microwave and qubit measurement data.
- Modeling of loss mechanisms using resonant absorption by two-level defects.
- Fabrication and testing of redesigned phase qubits with improved dielectrics and smaller junctions.
Main Results:
- Dielectric loss from two-level defects accurately models observed decoherence in various qubit designs.
- Significant reduction in dielectric loss achieved through optimized materials and junction fabrication.
- A redesigned phase qubit demonstrated a 20-fold improvement in energy relaxation rate.
Conclusions:
- Dielectric loss from two-level states is a critical factor limiting superconducting qubit coherence.
- Employing high-quality dielectrics and minimizing junction area are effective strategies for mitigating this loss.
- Improved qubit performance paves the way for advanced quantum algorithms and multiqubit gates.