Localization and reduction of superconducting quantum coherent circuit losses

Nitrogen Plasma Passivated Niobium Resonators for Superconducting Quantum Circuits

“…We suspect that this could be due to their susceptibility to trapped vortices and radiation to lossy regions inside the package. The Q HP i values of our resonators are lower compared to other similar studies 12,23 , which we attribute to specific details of the sample package 33,36 and measurement setup.…”

“…The microwave loss of state-of-the-art superconducting materials at low excitation powers is ultimately limited by two-level-system (TLS) defects that primarily reside at the metal-air (MA), metal-substrate (MS), and substrate-air (SA) interfaces 11 . For Nb resonators, most of the TLSs reside in the oxide layer at the MA interface and the removal of the oxide 12 produces CPW resonators with single-photon internal quality factor Q i up to 5 million and filling factor adjusted two-level-system loss tangent Fδ TLS down to 9 • 10 −8 . However, the oxide grows back following a Cabrera-Mott 13 behavior within several hours, reintroducing TLSs at the MA interface 14,15 (Fig.…”

Ternary Metal Oxide Substrates for Superconducting Circuits

“…41 Buffered oxide etch (BOE) has been used to strongly suppress TLS losses at the exposed substrate-air interface. 6 As BOE is a widely applied surface preparation technique for LaAlO 3 (and related perovskite surfaces) wet chemical post-processing may reduce the impact of TLS on our devices. 19 Furthermore, we note that after BOE processing, the acid needs to be neutralized by rinsing in deionized water.…”

“…1 Currently, material and interfacial losses are the most prominent factors hindering the development of a useful quantum computer. 2,6 Alternative substrate materials for superconducting devices have been most investigated in relation to hybrid quantum devices, where superconducting elements are coupled to optical, mechanical, or spin degrees of freedom. Superconducting circuitry has been fabricated on substrates such as amorphous SiN x 7 , Y 2 SiO 5 8 , a) Correspondence email address: a.fedorov@uq.edu.au b) Correspondence email address: p.jacobson@uq.edu.au GaAs 9,10 , GaN 11 , SiGe 12 , and diamond 13 with the general trend being equivalent or lower measures of resonator quality factor (or qubit coherence times) compared to state-of-the-art devices grown on silicon or sapphire.…”

Identification of different types of high-frequency defects in superconducting qubits

“…TLS defects are ubiquitous in the current generation of superconducting qubits: in the most commonly used method of Josephson junction fabrication, a junction tunnel barrier consists of an amorphous layer of aluminum oxide that hosts a large number of TLS defects [21,26]. Besides, the microwave absorption due to TLS defects formed in various oxide layers is one of the major mechanisms limiting Q-factors of microwave superconducting resonators [40,41], including superconducting 3D cavities which are used for quantum memory applications and bosonic quantum computing [42][43][44]. Normally, it is assumed that the qubit-defect interaction is caused by an electric-field coupling between an electric dipole associated with a charge TLS defect and a microwave electric field generated across a Josephson junction [14].…”