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https://www.nwo-i.nl/nwo-domein-enw/onderzoeksprogrammas/vrije-programmas/nr-i39-scalable-circuits-of-majorana-qubits-with-topological-protection/

Geprint op :
17 december 2018
20:58:09

Number

i39.

Title (code)

Scalable Circuits of Majorana Qubits (SCMQ)

Executive organisational unit

BUW

Programme management

Prof.dr.ir. L.P. Kouwenhoven

Duration

2014 – 2018

Cost estimate

M€ 16.2

Partner(s)

Microsoft

 

 

Concise programme description

Objectives
The potential realization of a quantum computer depends on the ability to suppress decoherence. One of the most promising proposed designs is based on so-called Majorana-state qubits. The longterm objective of this Industrial Partnership Programme is to develop scalable Majorana circuits of qubits with topological protection. The main scientific challenge is to demonstrate non-Abelian statistics through braiding, using circuits of Majorana qubits. In the future these topologically protected qubits are a possible building block for large-scale quantum computing.

Background, relevance and implementation
The promise of using Majoranas for scalable quantum circuits is that quantum decoherence can be circumvented by using topological protection. The topological protection is guaranteed as long as the fermionic parity of the system remains constant; i.e. the number of electrons in the system has to remain either an even or an odd number. This parity can be viewed as a qubit and can be denoted as the 'Majorana state'. Qubit operations involve exchanging different Majoranas around each other, called a 'braiding operation'. Strikingly, the expected exchange statistics is not fermionic, nor bosonic, but instead 'non-Abelian'. It is this non-Abelian statistics that makes these Majoranas so interesting. First, of all it would be the first (quasi) particle ever to show non-Abelian statistics. Second, the non-trivial exchange statistics provide a mean for manipulating quantum states useful for quantum computation. Most importantly, and absolutely stunning, is the notion that as long as topological protection works the Majorana state cannot decohere, i.e. quantum mechanics without decoherence!

The experimental challenge is to control parity conservation. Even-odd parity effects were studied in the '90's on superconducting nanostructures employing the stabilizing effect of Coulomb blockade. The current challenge is to repeat these experiments, however, Coulomb blockade cannot be used since this interaction in fact provides a coupling between different parities. We therefore have to control even-odd occupations of an open system.

Microsoft has chosen topologically protected qubits as their approach towards large scale quantum computing. The collaboration between Microsoft and the Kouwenhoven group at TU Delft was established in 2010. An earlier FOM-Microsoft IPP (TQC , nr. i26) was already granted and currently running, and resulted in the first discovery of the Majorana fermion. The current IPP puts a strong emphasis on technology development and making the transition from individual Majorana samples towards Majorana circuits.

Remarks
The final evaluation of this programme will consist of a self-evaluation initiated by the programme leader and is foreseen in 2018.