On-chip programmable circulator for scalable superconducting qubit readout

About the project

Every superconducting quantum computer's readout chain relies on bulky, magnetic ferrite circulators that block noise from reaching qubits, but can't be miniaturised or scaled. This project designs, fabricates, and tests a reconfigurable, on-chip, magnet-free circulator using space-time-modulated Josephson junctions, programmable in real time for next-generation AI-driven quantum control systems.

Reading out a superconducting qubit without destroying its quantum state requires strict nonreciprocity: probe signals must reach the qubit, while reflected or amplifier-generated noise must be blocked from travelling back. Today this is achieved with ferrite-based circulators, bulky, magnetic, fixed-response components that cannot be integrated and dominate the physical footprint and cost of the readout wiring as qubit counts scale toward hundreds or thousands.

This project addresses that bottleneck by developing a fundamentally new class of on-chip hardware: a nonreciprocal circulator based on space-time-modulated superconducting Josephson junctions, using their nonlinearity to break time-reversal symmetry without any magnetic material. Because the modulation is electronically controlled, the circulator's isolation, bandwidth, and routing can be reconfigured and programmed in real time, a key advantage over static ferrite devices, and a natural fit for next-generation quantum control systems that adapt readout and calibration on the fly.

You will develop theoretical and circuit models of space-time-modulated Josephson circuits for on-chip, programmable circulation; design and simulate candidate circulator architectures optimised for compatibility with standard qubit readout chains; and fabricate prototype devices, characterising isolation, noise performance, reconfigurability, and readout fidelity through cryogenic microwave measurements benchmarked against conventional ferrite circulators.

This research targets a bottleneck recognised across the quantum computing community as a key barrier to scaling qubit readout, offering a compact, magnet-free, and programmable route to denser, AI-compatible quantum processors. You'll gain expertise in superconducting circuit design, nonreciprocal electromagnetics, nanofabrication, and cryogenic microwave engineering, within a vibrant research team with strong industrial and academic collaborations.

Dr Sajjad Taravati

• Metamaterials/metasurfaces/antennas
• Electromagnetics/telecommunications
• Superconducting quantum circuits

Entry requirements

You must have at least a UK 2:1 honours degree or its international equivalent .

Fees and funding

Funding is available on a competitive basis through the EPSRC Centre for Doctoral Training in Quantum Technology Engineering at the University of Southampton.

UK students receive a 4 year UKRI TechFirst tax-free stipend of £30,000 per year. Studentships at the UKRI minimum rate are available for EU, Horizon Europe and International students.

Overseas students who have or are seeking external funding are welcome to apply.

While undertaking your research project, you'll also receive substantial training in scientific, technical and commercial skills.

How to apply

Apply now

Please apply via the online portal and select:

Applications should include:

• Academic year: 2027/28
• If you will be full time or part time
• Faculty: Engineering and Physical Sciences
• Search for PhD Quantum Tech Eng
• Add the name of the supervisor in section 2 of the application
• your CV (resumé)
• 2 academic references
• degree transcripts and certificates to date

Faculty of Engineering and Physical Sciences

For questions about applying, email the Centre for Doctoral Training in Quantum Technology Engineering (qte@soton.ac.uk) .

Project leader

For an initial conversation, email Dr Sajjad Taravati (S.Taravati@soton.ac.uk) .

Research areas