Annual report FOM programme nr. i26 'Topological quantum computation' Foundation for Fundamental Research on Matter

Size: px

Start display at page:

Download "Annual report FOM programme nr. i26 'Topological quantum computation' Foundation for Fundamental Research on Matter"

Angel Benson
5 years ago
Views:

FOM 14.0233 Annual report 2013 FOM programme nr. i26 'Topological quantum computation' Foundation for Fundamental Research on Matter www.fom.

1 FOM Annual report 2013 FOM programme nr. i26 'Topological quantum computation' Foundation for Fundamental Research on Matter An electron microscopy image of a nanowire junction on which electrical contacts have been made. In the future such a junction can be used to exchange the position of Majorana particles. This exchange of position is an important step towards understanding the characteristics of Majorana particles. May 2014

2 Content 1. Scientific results Added value of the programme Personnel Publications Valorisation and outreach... 4 Fact sheet as of 1 January Historical overview of input en output... 7 PhD defences... 7 Patents (new/changes)... 7 Overview of projects and personnel... 8 Workgroup FOMD

3 1. Scientific results 2013 The current state of the art in Majorana research is the observation of zerobias anomalies. This signature for Majoranas has been observed by several research groups and has been reproduced in many different device geometries. An important next step is to demonstrate that Majoranas can have topological properties. The topological protection in this case corresponds to an even or odd parity in the particle number in the device structure. In other words, do we have an even or an odd number of electrons in our nanowiresuperconductor devices? Evenodd parities have been measured in the midnineties in superconducting Coulomb blockade devices. The electron number was stabilized by a charging energy and uncontrolled fluctuations (known as quasiparticle poisoning) could be suppressed to timescales of microseconds. The challenge for Majorana devices is twofold. First, one cannot make use of a charging energy to stabilize the parity. Second, the evenodd physics has to be reinvented in superconducting materials that can sustain a magnetic field of order 1 Tesla. All Coulomb blockade devices have been done on Aluminum superconductors whereas our Majorana devices are built upon NbTiN. This year we have developed Josephson tunnel junctions with NbTiN islands. We have measured the quasiparticle poisoning timescale to be of order milliseconds. This is ~1000 times better compared to similar Al structures which is most likely due to the larger superconducting gap in NbTiN. We believe that in the near future we can extend our structures with additional quasiparticle traps and increase the timescale towards seconds. This long timescale is a very positive indication for the lifetime of a Majorana qubit. Majorana qubits can be realized in crosses of nanowires. In collaboration with the group of prof. Bakkers (TU/e) we have developed nanowire crosses. We have shown that the interface at the cross is epitaxial. This is confirmed in transport measurements that show a high conductance around the corner in a cross. We have also shown supercurrents flowing around the corner. Altogether we believe that our chosen approach towards braiding of Majoranas remains very promising. 2. Added value of the programme This IPP programme comes with a partnership with the Microsoft Station Q team that is headed by Dr. M. Freedman. This Q team is of exceptional quality and all meetings are very inspiring. 3. Personnel Everything is on track. Maybe the graduate students on this project may need an extension of several months for graduating. 3

4 4. Publications We have published a coverarticle on nanocrosses in Nature Nanotechnology, see picture. 5. Valorisation and outreach Lowlands University, August Paradiso lezing, May

5 Fact sheet as of 1 January 2014 FOM /5 datum: APPROVED INDUSTRIAL PARTNERSHIP PROGRAMME Number I26. Title (code) Executive organisational unit Programme management Topological quantum computation (TQC) BUW Prof.dr.ir. L.P. Kouwenhoven Duration Cost estimate M 4.0 Partner(s) Microsoft Concise programme description a. Objectives The realization of a quantum computer depends on the suppression of decoherence. Most qubit designs have ways to protect the informationcarrying quantum state as much as possible but the protection is never complete. This makes the lifetime of a quantum superposition finite and qubit operations subject to errors. There is one exception to this inherent obstacle: topologically protected qubits; in short topqubits. The intrinsic design of topqubits is such that deformations do not change the qubit state. This intrinsic protection is the same as the protected windingnumber of a belt with a single twist; deformations without breaking the belt cannot undo a single twist. It is obviously advantageous to build a complex quantum computer based on infinitely lived qubit states. Topqubits have yet to be realized and currently exist only on paper in various theoretical proposals. Nevertheless, Microsoft Station Q has chosen to focus their qubit activities entirely on this approach. This IPP proposes to realize topologicallyprotected qubits in nanoscale solid state devices. b. Background, relevance and implementation Recent theoretical proposals have developed new schemes for topqubits based on nanodevices with semiconductor nanowires and superconducting electrodes. It turns out that the leading proposals by Lutchyn et al. (2010) and Oreg et al. (2010) are based on previously realized devices (2006) by the Kouwenhoven group. The Kouwenhoven group thus has all the necessary expertise for upgrading their earlier devices into topqubit devices. For this reason Microsoft Station Q intends to finance experimental research in Kouwenhoven's group. This IPP aims at understanding and solving various scientific questions concerning the character of topological phases and states in condensed matter systems. The motivation of addressing these questions is the technological goal of a new form of computing, which is based on two new ingredients: quantum mechanics and topology. The realization of a fullscale quantum computer falls outside the timescale of this IPP. Within this program we focus on the initial required steps: the 5

6 realization and manipulation of topqubits based on the development of solid state Majorana Fermions. Within the first tranche of this programme signatures of Majorana Fermions have been observed in 2012 ( /science ). Funding salarispeil cao per bedragen in k < > 2019 Totaal FOMbasisexploitatie FOMbasis investeringen Doelsubsidies NWO Doelsubsidies derden Microsoft *) TKItoeslag Totaal *) Microsoft draagt in totaal k$ bij. De exacte bedragen in euro's worden bepaald volgens de koers op de dag dat de middelen worden overgemaakt. Daarnaast draagt Microsoft ca. 35 k$ in kind bij Source documents and progress control a) Original programme proposal: FOM ), FOM ), FOM ) b) Ex ante evaluation: FOM ), FOM ), FOM ), FOM ) c) Decision Executive Board: FOM ), FOM ), FOM ) d) Contracts: FOM ), FOM ,2), FOM ), FOM ), FOM ), FOM ), FOM ) 1) concerns first tranche 2) concerns second tranche 3) concerns third tranche Remarks The final evaluation of this programme will consist of a selfevaluation initiated by the programme leader and is foreseen in MvdH par. HOZB Subgebied: 100% NANO 6

7 Historical overview of input en output personnel (in fte) finances* (in k ) Input WP/V WP/T PhD NWP ,115 Output PhD theses refereed publications other publications & patents presentations * After closing the financial year. PhD defences 2012 None None. Patents (new/changes) 2013 None. 7

8 Overview of projects and personnel Workgroup FOMD41 Leader Organisation Project leader Programme Project (title + number) Prof.dr.ir. L.P. Kouwenhoven Delft University of Technology Prof. Y. Nazarov Topological quantum computation Topological quantum computation 5 12TQC05 FOM employees on this project Name Position Start date End date M.T. Wimmer postdoc 01 October September 2018 Leader Organisation Programme Project (title + number) Prof.dr.ir. L.P. Kouwenhoven Delft University of Technology Topological quantum computation Topological quantum computation 3 12TQC03 FOM employees on this project Name Position Start date End date S. Plissard postdoc 01 April November 2013 O. Gul PhD 01 January December 2016 E.A. Laird postdoc 15 November March 2013 Leader Organisation Programme Project (title + number) Prof.dr.ir. L.P. Kouwenhoven Delft University of Technology Topological quantum computation Topological quantum computation 1 11TQC01 FOM employees on this project Name Position Start date End date E.A. Laird postdoc 15 October November 2012 D.B. Szombati PhD 01 September August 2015 K. Zuo PhD 01 July November

Annual report FOM programme nr. i26 'Topological quantum computation' Foundation for Fundamental Research on Matter

Annual report FOM programme nr. i26 'Topological quantum computation' Foundation for Fundamental Research on Matter FOM 15.0320 Annual report 2014 FOM programme nr. i26 'Topological quantum computation' Foundation for Fundamental Research on Matter www.fom.nl Cooperpair Box with band gap engineering of the superconducting