Adiabatic two-qubit gates in capacitively coupled quantum dot hybrid qubits

Abstract

The ability to tune qubits to flat points in their energy dispersions ("sweet spots") is an important tool for mitigating the effects of charge noise and dephasing in solid-state devices. However, the number of derivatives that must be simultaneously set to zero grows exponentially with the number of coupled qubits, making the task untenable for as few as two qubits. This is a particular problem for adiabatic gates, due to their slower speeds. Here, we propose an adiabatic two-qubit gate for quantum dot hybrid qubits, based on the tunable, electrostatic coupling between distinct charge configurations. We confirm the absence of a conventional sweet spot, but show that controlled-Z (CZ) gates can nonetheless be optimized to have fidelities of ∼99% for a typical level of quasistatic charge noise (σε 1 µeV). We then develop the concept of a dynamical sweet spot (DSS), for which the time-averaged energy derivatives are set to zero, and identify a simple pulse sequence that achieves an approximate DSS for a CZ gate, with a 5× improvement in the fidelity. We observe that the results depend on the number of tunable parameters in the pulse sequence, and speculate that a more elaborate sequence could potentially attain a true DSS.

Progress toward a capacitively mediated CNOT between two charge qubits in Si/SiGe

“…Towards a two-qubit gate The capacitive interaction can also be used to drive one qubit conditionally on the state of the other as has been demonstrated experimentally in GaAs charge qubits 11 and proposed theoretically in Si/SiGe QDHQs 19 . To demonstrate conditional rotations, we designate the LDD the control qubit and the RDD the target.…”

“…In Si-based quantum dot devices, a strong 14 and tunable 15 capacitive interaction between double dots has been demonstrated and used to perform qubit control conditionally on the state of a classical two level system 16 . The strength of this interaction makes it a promising candidate for coupling qubits that have a tunable charge dipole moment such as the quantum dot hybrid qubit (QDHQ) [17][18][19] . Fast, multi-qubit control presents a number of challenges, however, such as pulse synchronization across a device.…”

Implementation of Geometric Quantum Gates on Microwave‐Driven Semiconductor Charge Qubits

“…[ 44 ] Since the non‐Abelian GQGs are using the state space more than two‐level structure, it is usually implemented in the three‐level system. [ 45–61 ] On the other hand, both the Abelian and non‐Abelian GQGs can be implemented by using the adiabatic [ 31,32,62–66 ] or non‐adiabatic [ 67,68 ] evolution of quantum states. The non‐adiabatic GQGs have attracted much more interest compared to the adiabatic approach, as the latter requires an overly long gating time that is impractical in experiments.…”

Minimal two-body quantum absorption refrigerator

“…In this article, we demonstrate that the absorption refrigeration can be obtained in a simpler setup, namely a qubit-qubit system with ZZ coupling. Notably, ZZ-coupling between two qubits has been experimentally realized in circuits ranging from qubits based on quantum dots to Josephson junctions 40,41 . An electronic version of our set up based on Coulomb coupled quantum dots was studied in Ref.…”