Superconductor–semiconductor hybrid-circuit quantum electrodynamics

Abstract

| Light-matter interactions at the single particle level have generally been explored in the context of atomic, molecular, and optical physics. Recent advances motivated by quantum information science have made it possible to explore coherent interactions between photons trapped in superconducting cavities and superconducting qubits. Spins in semiconductors can have exceptionally long spin coherence times and can be isolated in silicon, the workhorse material of the semiconductor microelectronic industry. Here, we review recent advances in hybrid "super-semi" quantum systems that coherently couple superconducting cavities to semiconductor quantum dots. We first present an overview of the underlying physics that governs the behavior of superconducting cavities, semiconductor quantum dots, and their modes of interaction. We then survey experimental progress in the field, focusing on recent demonstrations of cavity quantum electrodynamics in the strong coupling regime with a single charge and a single spin. Finally, we broadly discuss promising avenues of future research. Figure 5 | Strong spin-photon coupling. a | Top left panel: SEM image of a Si/SiGe DQD used to achieve spin-photon coupling. The orange dashed lines represent the locations of a pair of Co micromagnets fabricated on top of the DQD. Top right panel shows a cross-sectional view of the device. The application of an external magnetic field ext z B polarizes the micromagnets and creates an inhomogeneous magnetic field having a component M z B parallel to ext z B and a component M x B orthogonal to ext z B . M x B changes sign between the two dots, assuming a value of M ,L x B for the left dot and M ,R x B for the right dot. As a result, the quantization axis of an electron's spin (red arrows) is dependent on the electron's position. b | Energy level diagram of a single electron trapped in a DQD in the presence of an inhomogeneous magnetic field as a function of the DQD detuning energy ε. Here ↑ and ↓ denote the Zeeman-split spin-states of the electron, L (R) denotes the single-dot orbital state of the left (right) dot and -(+) denotes the molecular bonding (anti-bonding) state formed by the hybridization of the L and R states. c | Left panel: Cavity transmission amplitude A/A0 as a function of f and ext z B . Vacuum Rabi splitting with a frequency 2gs/2π = 11.0 MHz is observed at ext 92.2 z B = mT. Right panel: Increasing the detuning to ε = 40 µeV greatly reduces the vacuum Rabi splitting, allowing for electrical control of the spin-photon coupling rate. d | Strong spin-photon coupling using a high impedance NbTiN nanowire resonator. The cavity transmission coefficient |S21| is plotted as a function of f and ext z B . Inset: Scanning electron microscope image of a portion of the NbTiN nanowire resonator. Panels a, b and c are adapted from REF. 36 , Macmillan Publishers Limited. Panel d is adapted with permission from REF. 37 , AAAS.

Resonant exchange operation in triple-quantum-dot qubits for spin–photon transduction

“…Microwave (MW) photons in superconducting resonators are an attractive choice to mediate long-range spin entanglement by leveraging the powerful, highly successful techniques developed in circuit QED [6,7]. The fundamental challenge is to engineer sufficient spin-photon interaction: the small, fixed electron spin magnetic moment couples very weakly to the magnetic field of a MW photon [8], while spin qubits typically have very weak (but tunable) charge dipoles which suppress decoherence but also electrical interaction with photons.…”

Near-Field Scanning Microwave Microscopy in the Single Photon Regime

“…Feed-throughs at the 800 mK plate are designed to reduce the amount of thermal photons from hotter stages reaching the NSMM. tum metamaterials [21][22][23]. We discuss the limitations of our NSMM and the current limitations towards enabling it for these applications.…”

Toward Long-Range Entanglement between Electrically Driven Single-Molecule Magnets

“…Superconducting resonators are widely used to couple qubits based on superconducting circuits, [22][23][24] and have also been employed to couple remote electron spins. [25][26][27][28][29][30][31] They have high quality factors (Q ∼ 10 6 ) 32,33 and mature fabrication technology.…”

“…These are microwave-frequency resonators that possess a large kinetic inductance, and they have already been successfully coupled to spins in semiconductor quantum dots. 27,28,30 There are several reasons for choosing this particular type of resonator.…”