Download Ion Trap Quantum Technology for Quantum Computing

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.