High Coherence Superconducting Artificial Atom

Fluxonium [1] is a versatile multilevel superconducting artificial atom. It consists of a capacitor, a superinductor [2], and a Josephson junction in parallel. The three elements can be tuned to reach different regimes with... [ view full abstract ]

Fluxonium [1] is a versatile multilevel superconducting artificial atom. It consists of a capacitor, a superinductor [2], and a Josephson junction in parallel. The three elements can be tuned to reach different regimes with interesting physical properties, for example the metastable regime with milliseconds energy relaxation time [3, 4]. The circuit can be further controlled via an external magnetic flux: at integer and half-integer flux quantum, its spectrum is similar to those of transmon and flux qubit, respectively. 

Here we report coherence measurement of 0-1 transition in a 3D fluxonium circuit capacitively coupled to a box resonator. The circuit was fabricated by Al evaporation on an untreated silicon substrate. Energy relaxation time (T1) varies from a few microseconds at integer flux to over 100 microseconds at half-integer flux sweet spot, and coherence time (T2) approaches 2T1. Interestingly, T1 is limited at the sweet spot by dielectric loss with an effective loss tangent an order of magnitude higher than a recently reported value in transmon devices [5, 6]. Therefore, we expect that our fluxonium design has the potential to reach millisecond coherence once state-of-the-art fabrication techniques are employed. We discuss possible mechanisms that may limit T2 at the millisecond scale and ways to circumvent them.  

[1] V. Manucharyan, J. Koch, L. Glazman, M. Devoret, Science 326, (2009)

[2] V. Manucharyan, PhD thesis, (2012)

[3] Y-H. Lin, L. Nguyen, N. Grabon, J. San Miguel, N. Pankratova, V. Manucharyan, arXiv 1705.0787, (2017)

[4] N. Earnest, S. Chakram, Y. Lu, N. Irons, R. K. Naik, N. Leung, J. Lawrence, J. Koch, D. Schuster, arXiv 1707.00656, (2017)

[5] Y. Chu, C. Axline, C. Wang, T. Brecht, Y. Gao, L. Frunzio and R. Schoelkopf, Applied Physics Letters 109, (2016).

[6] C. Wang, C. Axline, Y. Gao, T. Brecht, Y. Chu, L. Frunzio, M. Devoret and R. Schoelkopf, Applied Physics Letters 107, (2015).