Coherent control of three-spin states in a triple quantum dot

Abstract

It has been suggested that triple quantum dots may provide additional tools and functionalities. These include encoding information either to obtain protection from decoherence or to permit all-electrical operation 5 , efficient spin busing across a quantum circuit 6 , and to enable quantum error correction using the three-spin Greenberger-Horn-Zeilinger quantum state. Towards these goals we demonstrate coherent manipulation of two interacting three-spin states. We employ the Landau-Zener-Stückelberg 7,8 approach for creating and manipulating coherent superpositions of quantum states 9 . We confirm that we are able to maintain coherence when decreasing the exchange coupling of one spin with another while simultaneously increasing its coupling with the third. Such control of pairwise exchange is a requirement of most spin qubit architectures 10 , but has not been previously demonstrated.Following the spin qubit proposal by Loss and DiVincenzo 10 and the electrostatic isolation of single spins in quantum dots (QDs) 11 and double quantum dots (DQDs) 12 , coherent manipulation was demonstrated in two-level systems based on single-spin up and down states 2 as well as two-spin singlet and triplet states 1 . Here we demonstrate coherent manipulation of a two-level system based on three-spin states. We employ the triple quantum dot (TQD) device layout shown in Fig. 1a, consisting of multiple metallic gates on a GaAs/AlGaAs heterostructure. The gates are used to electrostatically define three QDs in series within a two-dimensional electron gas 110 nm below the surface. The QDs are surrounded by two quantum point contact charge detectors (QPCs) 13 . The QPC conductance identifies the number of electrons in each QD and its derivative with respect to a relevant gate voltage maps out the device configuration stability diagram. We tune the device to the qubit operating electronic configuration, (N L ,N C ,N R ) = (1,1,1), between two spin-to-charge conversion regimes (1,0,2) and (2,0,1), where L, C and R refer to the left, centre and right QDs respectively. The detuning, ε, controls the energy difference between configurations (1,0,2), (1,1,1) and (2,0,1). The exchange coupling, J , depends on ε and the tunnel couplings.In this paper we concentrate on two scenarios. In the first scenario, at each point in the stability diagram the exchange coupling to the centre spin from one or both of the edge spins is minimal (that is, one edge spin resembles a passive spectator). This configuration is used as a control to confirm that our device maps onto two-spin results in this limit 9 . In the second scenario a true three-interacting-spin regime is achieved. (Results from a third intermediate regime are shown in the Supplementary Information.)

Non-Gaussian signatures and collective effects in charge noise affecting a dynamically decoupled qubit

“…Here we examine the validity range of the Gaussian approximation, as the number of fluctuators is increased, and its dependence on the number of control pulses. As current experimental efforts are focused on more complicated QD structures, such as two coupled double QDs, 26,35 and three-spin qubits in triple-dots, [36][37][38] the resulting larger devices are expected to have a noisier charge environment. Understanding how qubit decoherence scales with the number of TLFs is therefore important.…”

Entanglement switching via the Kondo effect in triple quantum dots

“…Three coherently coupled quantum dots with three spins attracted interest in the hope to construct a qubit using purely electrically gated manipulations [9,10]. Most recently, for a triple quantum dot (TQD) structure it was shown that bipolar spin blockade can become a relevant quantum coherent mechanism [11].…”

Information Processing with Electron Spins

“…These have been demonstrated repeatedly by numerous groups in the context of spintronic quantum computing [14][15][16][17][18][19][20][21][22][23][24][25][26][27]. It is currently a well-established art.…”