Patrick M. Leung

Coherent control of microwave pulse storage in superconducting circuits.

Coherent pulse control for quantum memory is viable in the optical domain but nascent in microwave quantum circuits. We show how to realize coherent storage and on-demand pulse retrieval entirely within a superconducting circuit by exploiting and extending existing electromagnetically induced transparency technology in superconducting quantum circuits. Our scheme employs a linear array of superconducting artificial atoms coupled to a microwave transmission line.

Low-loss surface modes and lossy hybrid modes in metamaterial waveguides

Abstract We show that waveguides with a dielectric core and a lossy metamaterial cladding (metamaterial-dielectric guides) can support hybrid ordinary-surface modes previously only known for metal-dielectric waveguides. These hybrid modes are potentially useful for frequency filtering applications as sharp changes in field attenuation occur at tailorable frequencies. Our results also show that the surface modes of a metamaterial-dielectric waveguide with comparable electric and magnetic losses can be less lossy than the surface modes of an analogous metal-dielectric waveguide with electric losses alone. Through a characterization of both slab and cylindrical metamaterial-dielectric guides, we find that the surface modes of the cylindrical guides show promise as candidates for all-optical control of low-intensity pulses.

Optical zeno gate: bounds for fault tolerant operation

In principle the Zeno effect controlled-sign gate of Franson et al (2004 Phys. Rev. A 70 062302) is a deterministic two-qubit optical gate. However, when realistic values of photon loss are considered its fidelity is significantly reduced. Here we consider the use of measurement based quantum processing techniques to enhance the operation of the Zeno gate. With the help of quantum teleportation, we show that it is possible to achieve a Zeno CNOT gate (GC-Zeno gate) that gives (near) unit fidelity and moderate probability of success of 0.8 with a two-photon to one-photon absorption ratio ? = 104. We include some mode-mismatch effects and estimate the bounds on the mode overlap and ? for which fault tolerant operation would be possible.

Improving the fidelity of optical Zeno gates via distillation

We have modeled the Zeno effect controlled-sign gate of Franson et al. [Phys. Rev. A 70, 062302 (2004)] and shown that high two-photon to one-photon absorption ratios,

Spectral effects of strong X(2) nonlinearity for quantum processing

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Slow light with three-level atoms in metamaterial waveguides

, are needed for high fidelity free-standing operation. Hence we instead employ this gate for cluster state fusion, where the requirement for

Electromagnetically controlled storage and retrieval for pulses propagating through a line of atoms

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Waveguide characteristics for arbitrary permittivity and permeability including for metamaterials

is less restrictive. With the help of partially offline one-photon and two-photon distillations, we can achieve a fusion gate with unity fidelity but nonunit probability of success. We conclude that for

Improving fidelity of skewed output states of optical zeno gates

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Quantum memory scheme based on optical fibers and cavities

, the Zeno fusion gate will out perform the equivalent linear optics gate.