Acceptor-induced bulk dielectric loss in superconducting circuits on silicon

The performance of superconducting quantum circuits is primarily limited by dielectric loss due to interactions with two-level systems (TLS). State-of-the-art circuits with engineered material interfaces are approaching a limit where dielectric loss from bulk substrates plays an important role. However, a microscopic understanding of dielectric loss in crystalline substrates is still lacking. In this work, we show that boron acceptors in silicon constitute a strongly coupled TLS bath for superconducting circuits. We discuss how the electronic structure of boron acceptors leads to an effective TLS response in silicon. We sweep the boron concentration in silicon and demonstrate the bulk dielectric loss limit from boron acceptors. We show that boron-induced dielectric loss can be reduced in a magnetic field due to the spin-orbit structure of boron. This work provides the first detailed microscopic description of a TLS bath for superconducting circuits, and demonstrates the need for ultrahigh purity substrates for next-generation superconducting quantum processors

Indistinguishable photons from an artificial atom in silicon photonics

Silicon is the ideal material for building electronic and photonic circuits at scale. Integrated photonic quantum technologies in silicon offer a promising path to scaling by leveraging advanced semiconductor manufacturing and integration capabilities. However, the lack of deterministic quantum light sources and strong photon-photon interactions in silicon poses a challenge to scalability. In this work, we demonstrate an indistinguishable photon source in silicon photonics based on an artificial atom. We show that a G center in a silicon waveguide can generate high-purity telecom-band single photons. We perform high-resolution spectroscopy and time-delayed two-photon interference to demonstrate the indistinguishability of single photons emitted from a G center in a silicon waveguide. Our results show that artificial atoms in silicon photonics can source single photons suitable for photonic quantum networks and processors

Phonon-protected superconducting qubits

The overhead to construct a logical qubit from physical qubits rapidly increases with the decoherencerate. Current superconducting qubits reduce dissipation due to two-level systems (TLSs) by using large device footprints. However, this approach provides partial protection, and results in a trade-off between qubit footprint and dissipation. This work introduces a new platform using phononics to engineer superconducting qubit-TLS interactions. We realize a superconducting qubit on a phononic bandgap metamaterial that suppresses TLSmediated phonon emission. We use the qubit to probe its thermalization dynamics with the phonon-engineered TLS bath. Inside the phononic bandgap, we observe the emergence of non-Markovian qubit dynamics due to the Purcell-engineered TLS lifetime of 34 μs. We discuss the implications of these observations for extending qubit relaxation times through simultaneous phonon protection and miniaturization

Mode Sensitivity Analysis of Subwavelength Grating Slot Waveguides

In this paper, we investigate the mode sensitivity (S-mode) of subwavelength grating slot (SWGS) waveguides. S-mode is an important parameter in various waveguide-based photonic circuits such as sensors, modulators, and thermally-controlled devices. It is a measure of the sensitivity of the waveguide effective index towards the refractive index perturbations in the cladding medium. The SWGS waveguide exhibits high mode sensitivity, as it combines sensitivity enhancement features of both slot and subwavelength grating waveguides. Finite-difference time-domain simulations are performed for the analysis, design, and optimization of the hybrid structure. The SWGS waveguide is incorporated into a Mach-Zehnder interferometer and fabricated on a silicon-on-insulator platform for the experimental estimation of S-mode. The measured S-mode value of 79% is consistent with the theoretical prediction of 83%