Topologically Protected Quantum States in Superfluid Fermi Gases
Abstract
AbstractTopologically Protected Quantum States in Superfluid Fermi GasesMartin W. ZwierleinProfessor of PhysicsCenter for Ultracold Atoms, Department of Physics, and Research Laboratory ofElectronics, Massachusetts Institute of TechnologyThe quest for robust quantum mechanical devices for sensing and quantum information,immune against environmental noise causing decoherence, has led to proposals of topologicalprotection of quantum information. The ideas require intricate topological states of matter, suchas topological superfluids or superconductors where fermion pairs carry non-zero angularmomentum or special fractional quantum Hall states. However, due to the immense difficultiesof creating such devices in a pristine fashion, so far no such topologically protected qubits havebeen observed.In this proposal we aim to demonstrate another type of topologically protected qubit: Andreevbound states inside the vortex cores of a (s-wave) two-dimensional fermion superfluid ofLithium-6. In contrast to the above proposals, quantum information here is stored locally, butstill robustly protected by two powerful agents: 1) The topological protection provided by thesuperfluid wavefunction ~ the fact that the phase winding around the vortex must be 2*Pi, so thatthe vortex cannot disappear unless the wavefunction becomes zero; and 2) the superfluid pairinggap Delta, which gaps out all single-particle excitations in the fermion superfluid. The remainingexcitations that can interact with the vortex are sound waves (phonons), but their number isvanishingly small at the temperatures we routinely achieve. Indeed, we have demonstrated vortexlifetimes in three-dimensional fermionic superfluids of several tens of seconds. This should becontrasted with the time-scale given by the pairing gap, corresponding to a few hundredmicroseconds, the minimum timescale at which Andreev states can be coherently manipulated.This yields a ratio of 105, which is more than sufficient to fulfill the criteria of useful quantumcomputation.An entire lattice of vortices in a 2D superfluid, such as we can create it via rotation,containing on the order of hundred vortices, can host many hundreds to thousands of Andreevstates. Apart from their potential to store quantum information, they also represent sensitivedetectors of superflow or equivalently of motion and rotation. Indeed, the energy differencebetween a pair of Andreev states directly depends on the relative velocity of the vortex withrespect to the bulk superfluid, allowing for a precision read-out of relative velocity.This proposal is centered on the creation, detection and manipulation of the Andreev boundstates inside vortex cores of a fermionic superfluid. Ways to entangle two such bound states, forinstance via braiding of vortices, could be explored beyond the three-year timescale of a standardgrant.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Mar 03, 2017
- Source ID
- N000141712257
Entities
People
- Martin W. Zwierlein
Organizations
- Massachusetts Institute of Technology
- Office of Naval Research
- United States Navy