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Ion Trap Quantum Technology for Quantum Computing & Networking Supervisors: Prof. David Lucas (Oxford University), (Primary Supervisor) & Prof. Richard Thompson (Imperial) [email protected], [email protected] www.physics.ox.ac.uk/users/iontrap Background: Laser-cooled trapped ions are one of the most promising technologies for building a quantum simulator or quantum computer, which could be one of the most dramatic technological developments of the 21st century. Such devices will only be realized if the qubits can be manipulated sufficiently precisely, and if the challenge of scaling the system up to a large enough number of qubits is addressed. At Oxford (primary location of project), we have demonstrated both the best qubits and best quantum logic gates in the world; see [1] and [2]. We have achieved a qubit coherence (memory) time of T2* 50 seconds, state-preparation and measurement precisions of >=99.95%, two-qubit gates with fidelity 99.9% and single-qubit gates with 99.9999% precision. These values significantly exceed the “fault-tolerant threshold” of 99%, below which quantum computing is not possible. We are presently aiming to scale up the system in a modular fashion, using several multi-zone ion traps networked by photonic links, as part of the £38M Oxford-led “Networked Quantum Information Technology” (NQIT) EPSRC-funded Hub. First-class students who are motivated to work with a team of talented researchers to tackle this formidable challenge are encouraged to apply. [1] T.P.Harty et al., Phys.Rev.Lett. 113, 220501 (2014); Phys.Rev.Lett. 117, 140501 (2016). [2] C.J.Ballance et al., Nature 528, 384 (2015); Phys.Rev.Lett 117, 060504 (2016). (a) (b) Fig.1: Ion trap technology: microfabricated “surface electrode” ion traps built at Oxford. Both traps were entirely designed, fabricated in-house, and characterized by Ph.D. students. (a) This chip trap was the first surface trap fabricated outside the U.S.; the inset shows a string of three calcium ions held in the trap each ion is used to store one qubit. (b) The first ion trap in the world to incorporate integrated microwave circuit elements (waveguides, couplers, resonant cavities): it is the first device in any technology to demonstrate all fundamental qubit operations with the precision necessary for building a quantum computer. First year project: One of the challenges in scaling up an ion trap system is the large number of laser systems required for manipulating thousands of separate qubits. The two ion species used at Oxford, Ca+ and Sr+, are almost unique in that all wavelengths can be obtained from solidstate diode lasers without the need for inefficient frequency-doubling systems. You will investigate the suitability of the latest generation of high-power (300mW) “Blu-Ray” diodes near 400nm wavelengths for quantum logic experiments, developing optical and/or electronic laser locking and switching methods. This will train you in relevant laser and electronics skills. Ph.D. project: There are three major projects currently underway: (1) the development of a cryogenic version of the microwave trap pictured in fig.1(b) in order to implement faster and higher precision two-qubit microwave-driven logic gates; (2) the laser-manipulation of mixedspecies ion crystals (calcium-43 and strontium-88 ions) in a 3D trap, for quantum networking of ion qubits via photonic interfaces – this will require the study of the physics of ion/photon entanglement and entanglement purification strategies; (3) the development of a segmented multi-zone trap in a miniaturized vacuum cell for use as a “node” in the modular scalable QC device. The specific choice of project will be made after the first year.