Showing 1–5 of 5 results for author: Cox, T

MEDA: Measurement-Efficient Disorder-Aware Majorana Zero Mode Detection in Realistic Devices

Authors: Nathan Jones, Binayyak Roy, Valentine Mohaugen, Ian Lewis, Toby Cox, Sumanta Tewari, Rong Ge

Abstract: Fault-tolerant topological quantum computing relies on identifying Majorana zero modes (MZMs), but reliable detection in realistic devices remains challenging. Conventional topological indicators are inherently biased in finite, disordered systems, blurring the distinction between true MZMs and trivial states. Furthermore, attempts to map these indicators to real observables via machine learning r… ▽ More Fault-tolerant topological quantum computing relies on identifying Majorana zero modes (MZMs), but reliable detection in realistic devices remains challenging. Conventional topological indicators are inherently biased in finite, disordered systems, blurring the distinction between true MZMs and trivial states. Furthermore, attempts to map these indicators to real observables via machine learning require dense, expensive conductance measurements, creating a severe scaling bottleneck. To simultaneously address topological bias and measurement limitations, we present MEDA: a Measurement-Efficient, Disorder-Aware framework for MZM detection in realistic devices. MEDA maps sparse, practically obtainable observables directly to the robust periodic disorder invariant (PDI). Using a novel sparse parameter regime, MEDA reduces measurement volume by 10x while maintaining predictive quality, even in moderate to strong disorder regimes that limit conventional methods. Furthermore, MEDA naturally prioritizes input features consistent with the topological gap protocol, demonstrating strong physical interpretability. △ Less

Submitted 16 August, 2026; v1 submitted 28 July, 2026; originally announced July 2026.

Comments: Accepted to 2026 IEEE International Conference on Quantum Computing and Engineering

Correlation effects in spin models in the presence of a spin bath

Authors: Álvaro Gómez-León, Tim Cox, Philip Stamp

Abstract: We analyze the effect of a bath of spins interacting with a spin system in terms of the equation of motion technique. We show that this formalism can be used with general spin systems and baths, and discuss the concrete case of a Quantum Ising model longitudinally coupled to the bath. We show how the uncorrelated solutions change when spin-spin correlations are included, the properties of the quas… ▽ More We analyze the effect of a bath of spins interacting with a spin system in terms of the equation of motion technique. We show that this formalism can be used with general spin systems and baths, and discuss the concrete case of a Quantum Ising model longitudinally coupled to the bath. We show how the uncorrelated solutions change when spin-spin correlations are included, the properties of the quasiparticle excitations and the effect of internal dynamics in the spin bath. △ Less

Submitted 20 September, 2019; v1 submitted 19 November, 2018; originally announced November 2018.

Comments: Main text and Appendix

Partitioned Density Matrices and Entanglement Correlators

Authors: Timothy Cox, Philip C. E. Stamp

Abstract: The density matrix of a non-relativistic quantum system, divided into $N$ sub-systems, is rewritten in terms of the set of all partitioned density matrices for the system. For the case where the different sub-systems are distinguishable, we derive a hierarchy of equations of motion linking the dynamics of all the partitioned density matrices, analogous to the "Schwinger-Dyson" hierarchy in quantum… ▽ More The density matrix of a non-relativistic quantum system, divided into $N$ sub-systems, is rewritten in terms of the set of all partitioned density matrices for the system. For the case where the different sub-systems are distinguishable, we derive a hierarchy of equations of motion linking the dynamics of all the partitioned density matrices, analogous to the "Schwinger-Dyson" hierarchy in quantum field theory. The special case of a set of $N$ coupled spin-$1/2$ "qubits" is worked out in detail. The equations are then rewritten in terms of a set of "entanglement correlators", which comprise all the possible correlation functions for the system - this case is worked out for coupled spin systems. The equations of motion for these correlators can be written in terms of a first-order differential equation for an entanglement correlator supervector. △ Less

Submitted 2 August, 2018; originally announced August 2018.

Journal ref: Phys. Rev. A 98, 062110 (2018)

Quantum Vortex Dynamics: Results for a 2-d Superfluid

Authors: Timothy Cox, Philip C. E. Stamp

Abstract: We model vortex dynamics in a 2-dimensional Bose superfluid using the Thompson-Stamp (TS) equations of motion, which describes both the classical Hall-Vinen-Iordanskii (HVI) dynamical regime and the fully developed quantum regime, and the crossover between them. The TS equations can be written in the form of a quantum Langevin equation. Analytic solutions are given for all of these regimes for a s… ▽ More We model vortex dynamics in a 2-dimensional Bose superfluid using the Thompson-Stamp (TS) equations of motion, which describes both the classical Hall-Vinen-Iordanskii (HVI) dynamical regime and the fully developed quantum regime, and the crossover between them. The TS equations can be written in the form of a quantum Langevin equation. Analytic solutions are given for all of these regimes for a single vortex in a 2-dimensional system. In the classical regime we include the vortex inertial and Langevin noise terms, which are dropped in the usual HVI analysis. In the quantum and crossover regimes the effect of memory terms is important, and leads to clear differences from the classical predictions. △ Less

Submitted 29 June, 2017; originally announced June 2017.

Comments: 14 pages, 8 figures

Inertial and fluctuational effects on the motion of a Bose superfluid vortex

Authors: T. Cox, P. C. E. Stamp

Abstract: We study the motion of a vortex under the influence of a harmonic force in an approximately two dimensional trapped Bose-condensed gas. The Hall-Vinen-Iordanskii equations, modified to include a fluctuational force and an inertial mass term, are solved for the vortex motion. The mass of the vortex has a strong influence on the time it takes the vortex to escape the trap. Since the vortex mass also… ▽ More We study the motion of a vortex under the influence of a harmonic force in an approximately two dimensional trapped Bose-condensed gas. The Hall-Vinen-Iordanskii equations, modified to include a fluctuational force and an inertial mass term, are solved for the vortex motion. The mass of the vortex has a strong influence on the time it takes the vortex to escape the trap. Since the vortex mass also depends on the trap size we have an additional dependence on the trap size in the escape time which we compare to the massless case. △ Less

Submitted 17 July, 2012; originally announced July 2012.

Comments: Submitted to J. Low. Temp. Phys