Möller, Gunnar, Cooper, N R, Gurarie, V (2011) Structure and consequences of vortexcore states in pwave superfluids. Physical Review B: Condensed Matter and Materials Physics, 83 . 014513. ISSN 01631829. (doi:10.1103/PhysRevB.83.014513)
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Official URL http://dx.doi.org/10.1103/PhysRevB.83.014513 
Abstract
It is now well established that in twodimensional chiral $p$wave paired superfluids, the vortices carry zeroenergy modes which obey nonabelian exchange statistics and can potentially be used for topological quantum computation. In such superfluids there may also exist other excitations below the bulk gap inside the cores of vortices. We study the properties of these subgap states, and argue that their presence affects the topological protection of the zero modes. In conventional superconductors where the chemical potential is of the order of the Fermi energy of a noninteracting Fermi gas, there is a large number of subgap states and the minigap towards the lowest of these states is a small fraction of the Fermi energy. It is therefore difficult to cool the system to below the minigap and at experimentally available temperatures, transitions between the subgap states, including the zero modes, will occur and can alter the quantum states of the zeromodes. Consequently, qubits defined uniquely in terms of the zeromodes do not remain coherent. We show that compound qubits involving the zeromodes and the parity of the occupation number of the subgap states on each vortex are still well defined. However, practical schemes taking into account all subgap states would nonetheless be difficult to achieve. We propose to avoid this difficulty by working in the regime of small chemical potential $\mu$, near the transition to a strongly paired phase, where the number of subgap states is reduced. We develop the theory to describe this regime of strong pairing interactions and we show how the subgap states are ultimately absorbed into the bulk gap. Since the bulk gap also vanishes as $\mu\to 0$ there is an optimum value $\mu_c$ which maximises the combined gap. We propose cold atomic gases as candidate systems where the regime of strong interactions can be explored, and explicitly evaluate $\mu_c$ in a Feshbach resonant $^{40}$K gas.
Item Type:  Article 

DOI/Identification number:  10.1103/PhysRevB.83.014513 
Uncontrolled keywords:  Physics of Quantum Materials, superfluid, BECBCS crossover, pwave, superconductor, vortices, subgap state, Majorana, topological quantum computation, Physics of Quantum Materials 
Subjects: 
Q Science > QC Physics > QC173.45 Condensed Matter Q Science > QC Physics > QC174.12 Quantum theory 
Divisions: 
Faculties > Sciences > School of Physical Sciences Faculties > Sciences > School of Physical Sciences > Functional Materials Group 
Depositing User:  Gunnar Moller 
Date Deposited:  29 Sep 2016 14:49 UTC 
Last Modified:  17 Jul 2019 11:15 UTC 
Resource URI:  https://kar.kent.ac.uk/id/eprint/55590 (The current URI for this page, for reference purposes) 
Möller, Gunnar:  https://orcid.org/0000000189860899 
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