Scalable, efficient ion-photon coupling with phase fresnel lenses for large-scale quantum computing

  • Authors:

  • E. W. Streed;B. G. Norton;J. J. Chapman;D. Kielpinski

  • Affiliations:

  • Centre for Quantum Dynamics, Griffith University, Nathan, QLD, Australia;Centre for Quantum Dynamics, Griffith University, Nathan, QLD, Australia;Centre for Quantum Dynamics, Griffith University, Nathan, QLD, Australia;Centre for Quantum Dynamics, Griffith University, Nathan, QLD, Australia

  • Venue:
  • Quantum Information & Computation
  • Year:
  • 2009

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Abstract

Efficient ion-photon coupling is an important component for large-scale ion-trap quantumcomputing. We propose that arrays of phase Fresnel lenses (PFLs) are a favorable opticalcoupling technology to match with multi-zone ion traps. Both are scalable technologiesbased on conventional micro-fabrication techniques. The large numerical apertures(NAs) possible with PFLs can reduce the readout time for ion qubits. PFLs also providegood coherent ion-photon coupling by matching a large fraction of an ion's emissionpattern to a single optical propagation mode (TEM00). To this end we have opticallycharacterized a large numerical aperture phase Fresnel lens (NA=0.64) designed for useat 369.5 nm, the principal fluorescence detection transition for Yb+ ions. A diffraction-limitedspot w0 = 350 ± 15 nm (1/e2 waist) with mode quality M2 = 1.08 ± 0.05 wasmeasured with this PFL. From this we estimate the minimum expected free space coherention-photon coupling to be 0.64%, which is twice the best previous experimentalmeasurement using a conventional multi-element lens. We also evaluate two techniquesfor improving the entanglement fidelity between the ion state and photon polarizationwith large numerical aperture lenses.