Reaching 10 ms single photon lifetimes for superconducting aluminum cavities (1302.4408v2)

Abstract: Three-dimensional microwave cavities have recently been combined with superconducting qubits in the circuit quantum electrodynamics (cQED) architecture. These cavities should have less sensitivity to dielectric and conductor losses at surfaces and interfaces, which currently limit the performance of planar resonators. We expect that significantly (>10^3) higher quality factors and longer lifetimes should be achievable for 3D structures. Motivated by this principle, we have reached internal quality factors greater than 0.5x10^9 and intrinsic lifetimes of 0.01 seconds for multiple aluminum superconducting cavity resonators at single photon energies and millikelvin temperatures. These improvements could enable long lived quantum memories with submicrosecond access times when strongly coupled to superconducting qubits.

• The paper reports achieving photon lifetimes up to 10.4 ms in 3D superconducting aluminum cavities using high-purity, chemically etched surfaces.
• The paper employs both rectangular and cylindrical designs to minimize dielectric and conductor losses, aligning with Mattis-Bardeen theory predictions.
• The paper’s findings pave the way for robust quantum memories in cQED systems by offering extended photon coherence and stable resonator performance.

Reaching 10 ms Single Photon Lifetimes for Superconducting Aluminum Cavities

This paper addresses the challenge of improving the quality factors and intrinsic lifetimes of microwave cavities used in circuit quantum electrodynamics (cQED). The paper focuses on superconducting aluminum cavities and aims to achieve longer lifetimes for single photons, utilizing three-dimensional (3D) designs as opposed to conventional planar resonators. The authors report the successful fabrication of aluminum cavities with internal quality factors exceeding 0.5 × 10$^9$, resulting in photon lifetimes of 0.01 seconds at millikelvin temperatures.

Technical Details and Results

3D cavitiy designs are advantageous chiefly due to their reduced sensitivity to dielectric and conductor losses at surfaces and interfaces, which are typically problematic in planar resonators. The paper cites historical precedents where superconducting niobium cavities achieved lifetimes on the order of seconds, thus setting a precedent for high-quality 3D resonators.

Key achievements in the paper include:

• Fabrication of both rectangular and cylindrical waveguide cavities from high-purity aluminum (ranging up to 99.9995% purity), with chemically etched surfaces to remove imperfections.
• Cylindrical resonators demonstrated the longest lifetimes, reaching up to 10.4 milliseconds.
• The reported cavity performance is markedly stable over a range of input microwave powers, showing negligible power dependence and limited sensitivity to quasiparticle densities at low temperatures.

The paper explores several physical phenomena impacting the cavities:

• Surface Dielectric Loss: It is found to be non-limiting in the 3D regime, as expected quality factors are significantly higher than achievable in planar resonators with similar dielectric properties.
• Surface Impedance: The temperature dependence of aluminum’s surface impedance aligns well with Mattis-Bardeen theory predictions, affirming that observed losses originate mainly from relationships intrinsic to the superconductor itself.

Implications and Future Directions

This exploration into 3D cavity resonators underscores their potential as robust quantum memories due to higher quality factors and longer lifetimes. The reduced impact of surface imperfections in these structures holds promise for quantum information processing systems, allowing stable and long-lived quantum states.

Further research could extend these findings by:

• Integrating superconducting qubits more effectively with these high-Q cavities, leveraging extended coherence times for more complex quantum operations.
• Exploring alternative material treatments or alloy compositions for even further reduction in surface losses.
• Investigating the mechanisms limiting the performance at ultra-low temperatures, such as parasitic magnetic fields and seam losses, to achieve optimal functionality.

In conclusion, this paper provides significant insights into the advancement of superconducting cavities in quantum systems. The authors’ methods demonstrate the viability of using aluminum 3D resonators to achieve unprecedented photon lifetimes in the microwave regime, thereby positioning these cavities as a powerful tool for quantum technologies.