Quantum Talks

Find out about our latest quantum talks.

Generation of fully phase controlled two-photos entangled states

Adrien Amour (Ion Trap Cavity-QED and Molecular Physics group)

26 August 2026

Control over the internal states of trapped ions makes them the ideal system to generate single and two-photon states. Coupling a single ion to an optical cavity enables efficient emission of single photons into a single spatial mode and grants control over their temporal shape, phase and frequency.

Using the long coherence time of the ion’s internal states and employing a scheme to protect the coherence of the ion-cavity interaction, we demonstrate the generation of a two-photon entangled state with full control over the phase. Initially, ion-photon entanglement is generated. A second photon is subsequently generated, mapping the ion’s state onto the second photon. By adjusting the drive field the phase of the entangled state can be fully controlled.

We implement this scheme in the most resource efficient way by utilizing a single 40Ca+ ion coupled to an optical cavity and demonstrate the generation of a two-photon entangled stated with full phase control with a fidelity of up to 82%.

Switchable low-noise permanent magnet gradients for long-wavelength trapped-ion quantum information

Caleb Burhan (Ion Quantum Technology group)

26 August 2026

Static magnetic field gradients can be used to couple the spin and motional states of trapped-ions, allowing for two-qubit gates using long-wavelength radiation. The use of permanent magnets to create such gradients give rise to much better noise specifications than the use of current carrying wires (CCWs), enabling much higher entanglement fidelities while reducing the required power consumption. The desire for scalability, as well as the need to switch fields off between gate and shuttling operations, has led to the development of trap-integrated current carrying wire methods of gradient generation.

Gradients produced by CCWs inevitably introduce current-dependant noise which must be mitigated with bulky low-noise current supplies. We present a method of generating magnetic field gradients with a novel magnetic field switching system. This “Saturable Electronic Reluctance Switch” (SERS) allows the field of a permanent magnet to be switched on and off by application of a current, but without any current dependence at the output field. This allows for fully stable output field akin to a permanent magnet allowing for high-fidelity two-qubit gates, but with the ability to switch the field on and off for shuttling operations within a QCCD architecture.

This method is the first bi-stable magnetic field switch, and can find applications in other areas of atomic and molecular physics such as micro-NMR imaging and neutral atom traps.