Decoherence of Majorana qubits by noisy gates

Schmidt, Manuel; Rainis, Diego; Loss, Daniel

doi:10.1103/physrevb.86.085414

Cited by 85 publications

(109 citation statements)

References 25 publications

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“…The escape rateγ could then vary between, say, 0.2 GHz and 2 GHz to vary between the adiabatic and the quenched regime. These frequencies should all lie above the decoherence rate of the Bogoliubov quasiparticle due to charge noise, which could be below 1 MHz [54].…”

Section: Discussionmentioning

confidence: 99%

Quench dynamics of fermion-parity switches in a Josephson junction

et al. 2015

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A Josephson junction may be driven through a transition where the superconducting condensate favors an odd over an even number of electrons. At this switch in the ground-state fermion parity, an Andreev bound state crosses through the Fermi level, producing a zero mode that can be probed by a point contact to a grounded metal. We calculate the time-dependent charge transfer between superconductor and metal for a linear sweep through the transition. One single quasiparticle is exchanged with charge Q depending on the coupling energies γ 1 ,γ 2 of the metal to the Majorana operators of the zero mode. For a single-channel point contact, Q equals the electron charge e in the adiabatic limit of slow driving, while in the opposite quenched limit Q = 2evaries between 0 and e. This provides a method to produce single charge-neutral quasiparticles on demand.

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Section: Discussionmentioning

confidence: 99%

Quench dynamics of fermion-parity switches in a Josephson junction

et al. 2015

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“…Very generally, no local measurement can read out the state of the qubit when the Majorana zero modes remain well separated from one another; the quantum information is encoded nonlocally through the island parities. Though certainly promising for the coherence of the qubit, it can still be prone to decoherence due to deviations from the ideal limit, as shown explicitly in numerous studies [96][97][98][99][100][101]. For example, a stray quasiparticle entering the islands from one of the outer superconductors can take the qubit out of the computational subspace.…”

Section: Prototype Topological Qubit Validation a Motivationmentioning

confidence: 99%

Milestones Toward Majorana-Based Quantum Computing

et al. 2016

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We introduce a scheme for preparation, manipulation, and read out of Majorana zero modes in semiconducting wires with mesoscopic superconducting islands. Our approach synthesizes recent advances in materials growth with tools commonly used in quantum-dot experiments, including gate control of tunnel barriers and Coulomb effects, charge sensing, and charge pumping. We outline a sequence of milestones interpolating between zero-mode detection and quantum computing that includes (1) detection of fusion rules for non-Abelian anyons using either proximal charge sensors or pumped current, (2) validation of a prototype topological qubit, and (3) demonstration of non-Abelian statistics by braiding in a branched geometry. The first two milestones require only a single wire with two islands, and additionally enable sensitive measurements of the system's excitation gap, quasiparticle poisoning rates, residual Majorana zero-mode splittings, and topological-qubit coherence times. These pre-braiding experiments can be adapted to other manipulation and read out schemes as well.

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“…In such cases, the energy splitting is exponentially suppressed in the regime L ξ s . This SC-mediated effect becomes significant if ξ s > ξ w , and, together with other decoherence mechanisms [27][28][29][30] , it could become an important issue. On the other hand, this effect also provides useful signatures that can help to identify MFs experimentally.…”

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confidence: 99%

Correlations between Majorana Fermions Through a Superconductor

et al. 2013

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We consider a model of ballistic quasi-one dimensional semiconducting wire with intrinsic spinorbit interaction placed on the surface of a bulk s-wave superconductor (SC), in the presence of an external magnetic field. This setup has been shown to give rise to a topological superconducting state in the wire, characterized by a pair of Majorana-fermion (MF) bound states formed at the two ends of the wire. Here we demonstrate that, besides the well-known direct overlap-induced energy splitting, the two MF bound states may hybridize via elastic tunneling processes through virtual quasiparticles states in the SC, giving rise to an additional energy splitting between MF states from the same as well as from different wires. Here we consider a model of a wire with Rashba SOI brought into contact with a bulk s-wave SC. Due to the interplay of proximity-induced superconductivity, SOI, and magnetic field, the wire is expected to enter a topological superconducting (TSC) phase for strong enough magnetic fields, and to host MF bound states localized at its two ends 21-23 . The energy of an isolated MF is pinned to the Fermi level inside the mini gap, due to its topological nature. In realistic finite-size wires the two end MF wave functions overlap, and such coupling leads to the splitting in energy of the otherwise doubly degenerate level. In most theoretical approaches, after one has calculated the proximity-induced gap in the wire, one usually forgets about the bulk SC and works with an effective model for the wire. The smallness of the energy splitting of the MF state, relevant for quantum computing purposes, is then determined by the relation between the wire length L and the MF localization length ξ w . Namely, in order to have an exponentially small splitting, it is necessary to require L ξ w . However, we show here that coupling between MFs can be established also through the SC, on a relevant length scale dictated by the coherence length ξ s in the SC (modified by inverse power-law corrections in L). In such cases, the energy splitting is exponentially suppressed in the regime L ξ s . This SC-mediated effect becomes significant if ξ s > ξ w , and, together with other decoherence mechanisms 27-30 , it could become an important issue. On the other hand, this effect also provides useful signatures that can help to identify MFs experimentally.Generally speaking, tunneling between normal leads via an s-wave SC can occur via elastic single-electron cotunneling processes or via local or crossed Andreev reflection 31-33 , which is a two-particle tunneling process. Tunneling in systems with MFs are different in that sense. Two MF states form a single complex fermionic state and coupling via the anomalous propagator of the SC is thus not possible. Still, we show here that hybridization between two MFs can be induced by coherent tunneling of electrons via virtual quasiparticle states of the SC.Model.-The setups considered here are schematically arXiv:1305.4187v2 [cond-mat.mes-hall]

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Decoherence of Majorana qubits by noisy gates

Cited by 85 publications

References 25 publications

Quench dynamics of fermion-parity switches in a Josephson junction

Quench dynamics of fermion-parity switches in a Josephson junction

Milestones Toward Majorana-Based Quantum Computing

Correlations between Majorana Fermions Through a Superconductor

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