Coherent electron transport in silicon quantum dots

Abstract

With silicon being the go-to material for spin qubits, and motivated by the demand of a scalable quantum computer architecture for fast and reliable quantum information transfer on-chip, we study coherent electron transport in a silicon double quantum dot. We first examine the valley-orbital dynamics in a silicon double dot, and discuss how to properly measure the tunnel couplings as well as the valley phase difference between two quantum dots. We then focus on possible phase and spin flip errors during spin transport across a silicon double dot. In particular, we clarify correction on the effective g-factor for the electron spin from the double dot confinement potential, and quantify the resulting phase error. We then study spin fidelity loss due to spin-valley mixing, which is a unique feature of silicon quantum dots. We show that a small phase correction between valleys can cause a significant coherence loss. We also investigate spin flip errors caused by either an external inhomogeneous magnetic field or the intrinsic spin-orbit coupling. We show that the presence of valleys makes it possible to have much broader (in terms of interdot detuning) level anticrossings compared to typical anti-crossings in, for example, a GaAs double dot, and such broad anti-crossings lead to amplification of spin flip errors. Lastly, we design a pulse sequence to suppress various possible spin flip errors by taking advantage of the multiple level anti-crossings in a silicon double dot and employing Landau-Zener transitions.

Multicore Quantum Computing

“…Previous theoretical treatments have given substantial attention to the ability of a single shuttling event to preserve an arbitrary input state's fidelity [52,[60][61][62][63]. However, a shuttling channel does not need to be able to shuttle arbitrary states to constitute a useful resource.…”

“…To investigate the dynamics of shuttling, it suffices to focus on the process of shuttling an electron from one QD to another in a DQD structure [62,63]. The Hamiltonian we have is similar to the static DQD Hamiltonian in Eq.…”

“…When the valley-orbit sector of Eq. ( 5) is rewritten in the {|± d } basis, the valley-conserving and valley-flipping tunnel couplings can be identified specifically as [62]…”

“…If the quality of the shuttled state is measured on the basis of fidelity, population loss into higher-energy states will degrade the quality of our Bell pairs unless recovered through appropriate calibrations [52,62], i.e., such a unitary evolution does not inherently destroy information but does rather introduce a coherent error. Although the coherent error introduced by the unitary evolution under our Hamiltonian in Eq.…”

Impact of the valley orbit coupling on exchange gate for spin qubits in silicon quantum dots

“…The study of this problem in single quantum dots have focused on the magnitude of valley splitting and interesting phenomena such as the spin-valley hotspot for spin relaxation [13,[33][34][35]. It has also been recognized in recent years that valley orbit coupling is generally complex, and its phase, particularly its variations across neighboring quantum dots, plays a crucial role in determining the tunnel coupling between dots [36][37][38][39][40][41][42][43][44].…”