The Simons Observatory (SO) is a new cosmic microwave background experiment being built on Cerro Toco in Chile, due to begin observations in the early 2020s. We describe the scientific goals of the experiment, motivate the design, and forecast its performance. SO will measure the temperature and polarization anisotropy of the cosmic microwave background in six frequency bands centered at: 27, 39, 93, 145, 225 and 280 GHz. The initial configuration of SO will have three small-aperture 0.5-m telescopes and one large-aperture 6-m telescope, with a total of 60,000 cryogenic bolometers. Our key science goals are to characterize the primordial perturbations, measure the number of relativistic species and the mass of neutrinos, test for deviations from a cosmological constant, improve our understanding of galaxy evolution, and constrain the duration of reionization. The small aperture telescopes will target the largest angular scales observable from Chile, mapping ≈ 10% of the sky to a white noise level of 2 µK-arcmin in combined 93 and 145 GHz bands, to measure the primordial tensor-to-scalar ratio, r, at a target level of σ(r) = 0.003. The large aperture telescope will map ≈ 40% of the sky at arcminute angular resolution to an expected white noise level of 6 µK-arcmin in combined 93 and 145 GHz bands, overlapping with the majority of the Large Synoptic Survey Telescope sky region and partially with the Dark Energy Spectroscopic Instrument. With up to an order of magnitude lower polarization noise than maps from the Planck satellite, the high-resolution sky maps will constrain cosmological parameters derived from the damping tail, gravitational lensing of the microwave background, the primordial bispectrum, and the thermal and kinematic Sunyaev-Zel'dovich effects, and will aid in delensing the large-angle polarization signal to measure the tensorto-scalar ratio. The survey will also provide a legacy catalog of 16,000 galaxy clusters and more than 20,000 extragalactic sources a .

We demonstrate enhanced relaxation and dephasing times of transmon qubits, up to ∼ 60 µs by fabricating the interdigitated shunting capacitors using titanium nitride (TiN). Compared to lift-off aluminum deposited simultaneously with the Josephson junction, this represents as much as a six-fold improvement and provides evidence that previous planar transmon coherence times are limited by surface losses from two-level system (TLS) defects residing at or near interfaces. Concurrently, we observe an anomalous temperature dependent frequency shift of TiN resonators which is inconsistent with the predicted TLS model.Long coherence times compared to logic gate times are necessary for building a fault tolerant quantum computer. In the case of superconducting qubits, coherence times have dramatically improved since the first demonstration 1 , by a factor of 10 3 planar circuits 2 and 10 4 using the 3D architecture 3,4 . Most of the improvements are attributable to a number of design changes including removing dissipation from the chip by coupling qubits to resonators (cQED architecture)5 , reducing the impact of charge noise 6 , and varying the geometry of the qubit shunting capacitor 2 . The natural question that arises is how further improvements will be possible, especially for the transmon qubit 6 , which has become a popular superconducting qubit design choice in the community.To answer this question it is instructive to formulate a hypothesis of what limits currently observed coherence times of transmons the majority of which are fabricated using lift-off aluminum deposited simultaneously with the Josephson junction. We believe the physical origin of dissipation is likely related to dielectric loss of amorphous materials 7 . Clever design improvements have reduced the impact of this loss mechanism but have not completely solved it. Specifically, two-level system (TLS) dielectric loss near interfaces appears to play a crucial role 8 . Experimental evidence to support this claim comes from (1) various design improvements and (2) materials improvements.First, quality factors are enhanced by geometric variations of CPW resonators 9-11 , qubit coherence times improve by increasing the size of the shunting capacitors 2 , as well as by employing the 3D architecture 3,4 . In fact, the recent advent of the 3D architecture highlights that ultra-small (∼ 100 nm) Josephson junctions likely do not play a key role in dissipation at the moment, and neither does bulk substrate loss (in the case of sapphire), leaving behind dielectric loss at interfaces ("surface losses") as a potential leading contributor to decoherence.Second, it was shown that quality factors of resonators using aluminum on sapphire can be improved by careful surface treatment prior to the deposition of the alua) Contributed equally to this work minum 12 . Similarly, titanium nitride (TiN) was also employed to improve the quality factors of resonators 13 , as well as for cQED devices demonstrating T 1 ∼ T 2 ∼ 11 µs 14 . However, these circuits used a large capac...

We present measurements of a topological property, the Chern number (C1), of a closed manifold in the space of two-level system Hamiltonians, where the two-level system is formed from a superconducting qubit. We manipulate the parameters of the Hamiltonian of the superconducting qubit along paths in the manifold and extract C1 from the nonadiabitic response of the qubit. By adjusting the manifold such that a degeneracy in the Hamiltonian passes from inside to outside the manifold, we observe a topological transition C1 = 1 → 0. Our measurement of C1 is quantized to within 2 percent on either side of the transition.

Thin films of TiN were sputter-deposited onto Si and sapphire wafers with and without SiN buffer layers. The films were fabricated into RF coplanar waveguide resonators, and internal quality factor measurements were taken at millikelvin temperatures in both the many photon and single photon limits, i.e. high and low power regimes, respectively. At high power, internal quality factors (Q i 's) higher than 10 7 were measured for TiN with predominantly a (200)-TiN orientation.Films that showed significant (111)-TiN texture invariably had much lower Q i 's, on the order of 10 5 . Our studies show that the (200)-TiN is favored for growth at high temperature on either bare Si or SiN buffer layers. However, growth on bare sapphire or Si(100) at low temperature resulted in primarily a (111)-TiN orientation. Ellipsometry and Auger measurements indicate that the (200)-TiN growth on the bare Si substrates is correlated with the formation of a thin, ≈ 2 nm, layer of SiN during the pre-deposition procedure. In the single photon regime, Q i of these films exceeded 8 × 10 5 , while thicker SiN buffer layers led to reduced Q i 's at low power.