Christopher James Axline

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Axline

First Name

Christopher James

ORCID

0000-0002-1708-3688

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Publications 1 - 7 of 7

Ac losses in field-cooled type I superconducting cavities
Catelani, Gianluigi; Li, K.; Axline, Christopher James; et al. (2022)
Superconductor Science and Technology
As superconductors are cooled below their critical temperature, stray magnetic flux can become trapped in regions that remain normal. The presence of trapped flux facilitates dissipation of ac current in a superconductor, leading to losses in superconducting elements of microwave devices. In type II superconductors, dissipation is well-understood in terms of the dynamics of vortices hosting a single flux quantum. In contrast, the ac response of type I superconductors with trapped flux has not received much attention. Building on Andreev's early work (Andreev 1967 Sov. Phys. JETP 24 1019), here we show theoretically that the dominant dissipation mechanism is the absorption of the ac field at the exposed surfaces of the normal regions, while the deformation of the superconducting/normal interfaces is unimportant. We use the developed theory to estimate the degradation of the quality factors in field-cooled cavities, and we satisfactorily compare these theoretical estimates to the measured field dependence of the quality factors of two aluminum cavities. We also identify a regime in which the dissipated power depends weakly on the Ginzburg-Landau parameter; this makes it possible to apply our findings to cavities made of other materials, such as niobium.
Error-Detected State Transfer and Entanglement in a Superconducting Quantum Network
Burkhart, Luke D.; Teoh, James D.; Zhang, Yaxing; et al. (2021)
PRX Quantum
Microwave photons are used to wire up modular quantum processors, but mitigating the effects of loss between modules remains a crucial challenge. We use a low-loss bus resonator to couple bosonic qubits across a superconducting network with protocols made robust to photon loss in the bus. We transfer a multiphoton qubit and track loss events, improving the fidelity to the break-even point with respect to the best uncorrectable encoding. We also demonstrate a entanglement protocol using Hong-Ou-Mandel interference and error detection to prepare a two-photon Bell state with fidelity 94% and success probability 0.79, halving the error obtained with a single photon. This network link also presents new opportunities for resource-efficient direct gates between modules.
Penning micro-trap for quantum computing
Jain, Shreyans; Sägesser, Tobias; Hrmo, Pavel; et al. (2024)
Nature
Trapped ions in radio-frequency traps are among the leading approaches for realizing quantum computers, because of high-fidelity quantum gates and long coherence times1,2,3. However, the use of radio-frequencies presents several challenges to scaling, including requiring compatibility of chips with high voltages4, managing power dissipation5 and restricting transport and placement of ions6. Here we realize a micro-fabricated Penning ion trap that removes these restrictions by replacing the radio-frequency field with a 3 T magnetic field. We demonstrate full quantum control of an ion in this setting, as well as the ability to transport the ion arbitrarily in the trapping plane above the chip. This unique feature of the Penning micro-trap approach opens up a modification of the quantum charge-coupled device architecture with improved connectivity and flexibility, facilitating the realization of large-scale trapped-ion quantum computing, quantum simulation and quantum sensing.
Physical coherent cancellation of optical addressing crosstalk in a trapped-ion experiment
Flannery, Jeremy; Matt, Roland; Huber, Luca Immanuel; et al. (2025)
Quantum Science and Technology
We present an experimental investigation of coherent crosstalk cancellation methods for light delivered to a linear ion chain cryogenic quantum register. The ions are individually addressed using focused laser beams oriented perpendicular to the crystal axis, which are created by imaging each output of a multi-core photonic-crystal fibre waveguide array onto a single ion. The measured nearest-neighbor native crosstalk intensity of this device for ions spaced by 5 μm is found to be ~10⁻². We show that we can suppress this intensity crosstalk from waveguide channel coupling and optical diffraction effects by a factor >10³ using cancellation light supplied to neighboring channels which destructively interferes with the crosstalk. We measure a rotation error per gate on the order of εₓ similar to 10⁻⁵ on spectator qubits, demonstrating a suppression of crosstalk error by a factor of >10². We compare the performance to composite pulse methods for crosstalk cancellation, and describe the appropriate calibration methods and procedures to mitigate phase drifts between these different optical paths, including accounting for problems arising due to pulsing of optical modulators.
Design, fabrication and characterisation of a micro-fabricated stacked-wafer segmented ion trap with two X-junctions
Decaroli, Chiara; Matt, Roland; Oswald, Robin; et al. (2021)
Quantum Science and Technology
We describe the implementation of a three-dimensional Paul ion trap fabricated from a stack of precision-machined silica glass wafers, which incorporates a pair of junctions for 2-dimensional ion transport. The trap has 142 dedicated electrodes which can be used to define multiple potential wells in which strings of ions can be held. By supplying time-varying potentials, this also allows for transport and re-configuration of ion strings. We describe the design, simulation, fabrication and packaging of the trap, including explorations of different parameter regimes and possible optimizations and design choices. We give results of initial testing of the trap, including measurements of heating rates and junction transport.
Industrially microfabricated ion trap with 1 eV trap depth
Auchter, Silke; Axline, Christopher James; Decaroli, Chiara; et al. (2022)
Quantum Science and Technology
Scaling trapped-ion quantum computing will require robust trapping of at least hundreds of ions over long periods, while increasing the complexity and functionality of the trap itself. Symmetric three-dimensional (3D) structures enable high trap depth, but microfabrication techniques are generally better suited to planar structures that produce less ideal conditions for trapping. We present an ion trap fabricated on stacked eight-inch wafers in a large-scale micro-electro-mechanical system microfabrication process that provides reproducible traps at a large volume. Electrodes are patterned on the surfaces of two opposing wafers bonded to a spacer, forming a 3D structure with 2.5 μm standard deviation in alignment across the stack. We implement a design achieving a trap depth of 1 eV for a ⁴⁰Ca⁺ ion held at 200 μm from either electrode plane. We characterize traps, achieving measurement agreement with simulations to within ±5% for mode frequencies spanning 0.6–3.8 MHz, and evaluate stray electric field across multiple trapping sites. We measure motional heating rates over an extensive range of trap frequencies, and temperatures, observing 40 phonons/s at 1 MHz and 185 K. This fabrication method provides a highly scalable approach for producing a new generation of 3D ion traps.
Suspending superconducting qubits by silicon micromachining
Chu, Yiwen; Axline, Christopher James; Wang, C.; et al. (2016)
Applied Physics Letters

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Christopher James Axline

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