We present microwave-frequency NbTiN resonators on silicon, systematically achieving internal quality factors above 1 M in the quantum regime. We use two techniques to reduce losses associated with two-level systems: an additional substrate surface treatment prior to NbTiN deposition to optimize the metal-substrate interface, and deep reactive-ion etching of the substrate to displace the substrate-vacuum interfaces away from high electric fields. The temperature and power dependence of resonator behavior indicate that two-level systems still contribute significantly to energy dissipation, suggesting that more interface optimization could further improve performance.Superconducting coplanar waveguide (CPW) microwave resonators are crucial elements in photon detectors 1 , quantum-limited parametric amplifiers 2,3 and narrow-band filters 4 , as well as read-out, interconnect and memory elements in quantum processors based on circuit quantum electrodynamics 5 . They also play a critical role in hybrid devices, connecting superconducting circuits with micro-and nanomechanical resonators 6,7 and solid-state spins 8,9 . In many quantum science and technology applications, resonators must operate in the quantum regime, requiring low temperatures to reach the ground state (thermal energy k B T small compared to the photon energy at resonance, hf r ) and single-photon excitation levels. Under these conditions, however, internal quality factors (Q i s) are typically substantially lower than their high-temperature or high-power values.In the quantum regime, the dominant loss mechanism for high-Q superconducting resonators can be attributed to parasitic two-level systems (TLSs) in the dielectrics 10,11 . TLSs may reside in the bulk substrate 11 , as well as in the metal-substrate, metal-vacuum and substrate-vacuum interfaces 10,[12][13][14][15][16][17][18] where electric fields may be large (see Ref. 19 and references therein for a recent review of material-related loss in superconducting circuits). Interface TLSs are common by-products of the fabrication process, often introduced by impurities associated with substrate surfaces 20,21 and etching chemistry 22 . To our knowledge, the best resonators reported to date 15 (Q i = 1.72 M at 6 GHz) are fabricated by epitaxially growing aluminum on sapphire substrates following careful surface preparation (high-temperature annealing in an oxygen atmosphere). For CPW resonators on silicon (Si) substrates, achieving Q i > 1 M in the quantum regime has proven challenging, with the best resonators reported in Ref. 23.In this letter, we present silicon-based, gigahertzfrequency CPW resonators with Q i systematically above 1 M in the quantum regime, fabricated from niobium titanium nitride (NbTiN) superconducting films. This performance is reached by optimizing two aspects of the fabrication. First, the substrate surface is treated with hexamethyldisilazane (HMDS) immediately prior to metal deposition to reduce losses associated with the metal-substrate interface. Second, we employ highl...

Circuit quantum electrodynamics has proven to be a powerful tool to probe mesoscopic effects in hybrid systems and is used in several quantum computing (QC) proposals that require a transmon qubit able to operate in strong magnetic fields. To address this we integrate monolayer graphene Josephson junctions into microwave frequency superconducting circuits to create graphene based transmons. Using dispersive microwave spectroscopy we resolve graphene’s characteristic band dispersion and observe coherent electronic interference effects confirming the ballistic nature of our graphene Josephson junctions. We show that the monoatomic thickness of graphene renders the device insensitive to an applied magnetic field, allowing us to perform energy level spectroscopy of the circuit in a parallel magnetic field of 1 T, an order of magnitude higher than previous studies. These results establish graphene based superconducting circuits as a promising platform for QC and the study of mesoscopic quantum effects that appear in strong magnetic fields.

Superconducting coplanar waveguide resonators that can operate in strong magnetic fields are important tools for a variety of high frequency superconducting devices. Magnetic fields degrade resonator performance by creating Abrikosov vortices that cause resistive losses and frequency fluctuations, or suppressing superconductivity entirely. To mitigate these effects we investigate lithographically defined artificial defects in resonators fabricated from NbTiN superconducting films. We show that by controlling the vortex dynamics the quality factor of resonators in perpendicular magnetic fields can be greatly enhanced. Coupled with the restriction of the device geometry to enhance the superconductors critical field, we demonstrate stable resonances that retain quality factors 10 5 at the single photon power level in perpendicular magnetic fields up to B ⊥ 20 mT and parallel magnetic fields up to B 6 T. We demonstrate the effectiveness of this technique for hybrid systems by integrating an InSb nanowire into a field resilient superconducting resonator, and use it to perform fast charge readout of a gate defined double quantum dot at B = 1 T.