Purcell filtering
Practical Quantum information processing requires fast and accurate qubit state measurement. However, a fast readout channel of the qubit state will also be a decay channel for quantum information. The enhancement of the spontaneous emission rate of qubits by its environment is known as the Purcell effect. In quantum systems, this will be place a maximum limit on the qubit lifetime. One method to limit such decay is through the use of a Purcell filter, such filters will limit the decay of the qubit state while still allowing access to the quantum information.
In our group, initial simulations have shown a filter design that allows the easy, modular addition onto quantum experiments. This project will involve understanding simulations from external collaborators and realising the device.
Reading:
Filter design: https://aip.scitation.org/doi/10.1063/1.4824489
General overview on cQED: https://arxiv.org/pdf/1904.06560.pdf
Alvise’s thesis: https://iqoqi.at/images/group/gk/master-theses/master_borgognoni.pdf
Seamless high Q cavity design
High-quality microwave resonators are a promising platform for quantum simulation and quantum information processing. Logical qubits encoded in superconducting cavities demonstrated advantages over Transmon qubits in coherence times and information capacity. Recent developments have shown the use of such resonators as Bosonic qubits in a push towards realising fault-tolerant quantum information processing with cQED devices.
Continuing on the success of a previous Master student project, our group has started multiple projects that uses coaxial quarter-wave cavities. We wish to further explore other cavity designs and cavity materials to test their suitability in our quantum information experiments. This project will involve the design, fabrication and measurement of such cavities.
Reading:
Paul’s thesis: https://iqoqi.at/images/group/gk/master-theses/improvin-the-quality-factor-of-coaxial-quarterwave-resonators.pdf
Markus’s thesis: https://iqoqi.at/images/group/gk/master-theses/Master_Thesis_Sifft.pdf
Recent paper from our group: https://arxiv.org/abs/2102.10016
Review on bosonic qubits https://arxiv.org/pdf/2008.13471.pdf
Other seamless high-quality cavity design: https://arxiv.org/abs/2010.16382
Waveguide QED
Superconducting qubits behave like atoms when they are interfaced with propagating photons. This gives rise to interesting quantum-effects like entanglement of spatially separated objects. We study these artificial atoms in photonic waveguides.
Projects
• Directional emission of microwave photons
• Anomalous photon transport
Reading material
https://arxiv.org/abs/2003.07300, https://arxiv.org/abs/1912.12233, https://www.nature.com/articles/s41586-019-1196-1, https://arxiv.org/abs/2004.01924, https://arxiv.org/abs/2007.03690, https://arxiv.org/abs/1407.6747
Reviews
https://arxiv.org/abs/1912.13012, https://arxiv.org/abs/1912.06234
Superconducting Magneto-Mechanics
How big can a quantum system be? To answer this question, we couple superconducting circuits magnetically to a mechanical oscillator. Ultimately, want to achieve quantum control over a mechanical mode consisting out of billion atoms.
Projects
• Optimizing high quality microwave resonators
• Characterizing magneto-mechanical coupling setups
Reading material
https://arxiv.org/abs/1912.05489, https://arxiv.org/abs/1912.08731, https://arxiv.org/pdf/1907.01418.pdf, https://arxiv.org/abs/1103.2144, https://arxiv.org/abs/1206.5562v1
Reviews
https://arxiv.org/abs/1303.0733, https://arxiv.org/abs/1106.2060