Indirect Interaction of Solid-State Qubits via Two-Dimensional Electron Gas

Abstract

We propose a mechanism of long-range coherent coupling between nuclear spin qubits in semiconductor-heterojunction quantum information processing devices. The coupling is via localized donor electrons which interact with the two-dimensional electron gas. An effective interaction Hamiltonian is derived and the coupling strength is evaluated. We also discuss mechanisms of decoherence and consider gate control of the interaction between qubits. The resulting quantum computing scheme retains all the control and measurement aspects of earlier approaches, but allows qubit spacing at distances of the order of 100 nm, attainable with the present-day semiconductor device technologies.

Exact gate sequences for universal quantum computation using theXYinteraction alone

“…For the quantum dot/cavity QED proposal, a two-dimensional triangular layout such as those in Figure 4 is attractive, while the three-dimensional layout of Figure 5 (with a static array of ancilla qubits in the second plane) appears well suited to the long-range coupling of nuclear spins proposed in Ref. [22]. Clearly, the ultimate layout in physical implementations will be subject also to experimental restrictions on the particular physical system at hand.…”

“…The XY exchange interaction underlies several experimental proposals for solid-state qubits, including quantum dot spins coupled by cavity QED [21] and nuclear spins coupled by a two-dimensional electron gas [22]. These different proposals involve diverse requirements on realizing physical coupling of the qubits.…”

“…This situation is relevant to several proposals for solid-state quantum computation, e.g., using quantum dot spins and cavity QED, [21] and using nuclear spins coupled by a two-dimensional electron gas [22]. In the following we give an explicit assessment of the trade-offs involved in implementing universal computation with the XY-interaction alone.…”

Universal quantum computation using exchange interactions and measurements of single- and two-spin observables

“…Since read-out is necessary, measurements are inevitable. Here we propose a minimalistic approach for universal quantum computation that is particularly well suited to the important class of spin-based QC proposals governed by exchange interactions [2,3,4,5,31,32], and other proposals governed by effective exchange interactions [33,34,35]. In particular, we show that UQC can be performed using only single-and two-qubit measurements and controlled exchange interactions, via gate teleportation.…”

“…However, unitary transformations are sometimes very challenging to perform. Two important examples are the exceedingly small photon-photon interaction that was thought to preclude linear optics QCs, and the difficult to execute single-spin gates in certain solid state QC proposals, such as quantum dots [2,3] and donor atom nuclear spins in silicon [4,5]. The problem with single-spin unitary gates is that they impose difficult demands on g-factor engineering of heterostructure materials, and require strong and inhomogeneous magnetic fields or microwave manipulations of spins, that are often slow and may cause device heating.…”