We employ an intermediate excited charge state of a lateral quantum dot device to increase the charge detection contrast during the qubit state readout procedure, allowing us to increase the visibility of coherent qubit oscillations. This approach amplifies the coherent oscillation magnitude but has no effect on the detector noise resulting in an increase in the signal to noise ratio. In this letter we apply this scheme to demonstrate a significant enhancement of the fringe contrast of coherent Landau-Zener-Stückleberg oscillations between singlet S and triplet T+ two-spin states.PACS numbers: 73.63. Kv, 73.21.La, The crucial step of spin qubit readout via spin to charge conversion is usually achieved through charge detection technology.[1] The maximum sensitivity is related to the difference (contrast) in the charge detection signal of the two charge state configurations. In this letter we demonstrate how this contrast can be amplified by a significant factor if a "state discriminating" relaxation process is introduced during the readout procedure. Since this modification only changes the charge detector contrast between the relevant qubit states, the signal to noise ratio is likewise enhanced.Spin qubits based on single, double or triple quantum dot circuits have been successfully demonstrated.[2-4] Following a coherent manipulation experiment the measurement is usually completed by reading out the final quantum state using a charge detector which is able to distinguish between the quantum spin states.We will concentrate on the qubit based on the singlet (S) and triplet (T + ) two-spin states recently demonstrated by Petta et al. [3] The corresponding oscillations are called Landau-Zener-Stückleberg (LZS) oscillations and are observed as fringes in the stability diagram or when plotted as a function of pulse duration, magnetic field or initial gate detuning. We stress that a similar readout advantage can be implemented for other spin qubit species. The experiments were made using a triple quantum dot device (see Fig. 1(a)).[4-6] During our measurements one quantum dot (R) was not coupled via exchange or tunnelling to the other two quantum dots making this effectively a two quantum dot experiment. [7] As a result we will use double quantum dot notation throughout. A schematic energy level diagram vs detuning is shown for a double dot in a magnetic field in Fig. 1(c). The two qubit states S and T + which differ in spin are coupled via the hyperfine interaction which creates an anticrossing in the energy level diagram.A generic S/T + spin qubit operation for this system * Electronic address: Andrew.Sachrajda@nrc.ca would proceed as follows. The quantum state preparation is first achieved by applying a pulse (in reality a combined pulse on gates 1 and 2) from the S(2,0) regime through the anticrossing to the (1,1) charge regime (where (n L , n C ) indicate the number of electrons, n L (n C ) in quantum dots L (C)). A suitable pulse rise time permits a superposition of the S and T + states to be generated via Landa...
Access and use of this website and the material on it are subject to the Terms and Conditions set forth at Three-spin coherent oscillations and interference Poulin-Lamarre, G.; Thorgrimson, J.; Studenikin, S. A.; Aers, G. C.; Kam, A.; Zawadzki, P.; Wasilewski, Z. R.; Sachrajda, A. S.http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/jsp/nparc_cp.jsp?lang=fr L'accès à ce site Web et l'utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D'UTILISER CE SITE WEB. NRC Publications Record / Notice d'Archives des publications de CNRC:http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/ctrl?action=rtdoc&an=21275844&lang=en http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/ctrl?action=rtdoc&an=21275844&lang=fr READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE.http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/jsp/nparc_cp.jsp?lang=en Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n'arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. Questions? Contact the NRC Publications Archive team atPublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information. NRC Publications Archive Archives des publications du CNRCThis publication could be one of several versions: author's original, accepted manuscript or the publisher's version. / La version de cette publication peut être l'une des suivantes : la version prépublication de l'auteur, la version acceptée du manuscrit ou la version de l'éditeur. For the publisher's version, please access the DOI link below./ Pour consulter la version de l'éditeur, utilisez le lien DOI ci-dessous.http://doi.org/10.1103/PhysRevB.91.125417Physical Review B -Condensed Matter and Materials Physics, 91, 12, 2015-03-16 PHYSICAL REVIEW B 91, 125417 (2015) Three-spin coherent oscillations and interference We utilize magnetic field dependencies to identify two hitherto unobserved quantum interference processes in a triple quantum dot circuit. The first observation involves the interplay of Landau-Zener-Stückelberg behavior from two separate anticrossings between two energy levels that anticross twice as a function of a detuning parameter. The second process involves quantum interference between all-exchange and hyperfine qubits activated in a three-spin system.
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