Compact Purcell Filter Design for Superconducting Qubit Readout & Current Activities
Discover the innovative research on compact Purcell filter designs for superconducting qubit readout at the University of Bologna. Explore solutions to enhance qubit measurement precision and reduce energy leakage, along with collaborations for creating more efficient architectures using JJ chains. Tools like QuCAT and Qiskit Metal are utilized to advance quantum circuit analysis and chip design methodologies. Stay updated on the latest developments in superconducting qubit technologies.
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Presentation Transcript
COMPACT PURCELL FILTER DESIGN FOR SUPERCONDUCTING QUBIT READOUT Simona Zaccaria, Antonio Gnudi DEI, Universit di Bologna
THE PROBLEM OF QUBIT MEASUREMENT THE PROBLEM OF QUBIT MEASUREMENT The state of the qubit is inferred from the measured frequency of the resonator There is additional leakage of the qubit s energy into the transmission line (Purcell effect) ? 2 = ?(??) Trade-off between qubit decay and readout measurement time
PURCELL FITLER PURCELL FITLER Solution: Solution: Add a filter to reduce the qubit decay at the qubit frequency 2 ? = ????(??)
CURRENT ACTIVITY CURRENT ACTIVITY Standard designs of Purcell filters use CPW resonators CPW resonators need cm-long lines Collaboration with Chalmers University (Simone Gasparinetti) to design compact architectures using inductors made of JJ chains Indeed, the non-linearity of a JJ chain is proportional to 1 ?2
CURRENT ACTIVITY CURRENT ACTIVITY Development of a first circuit with a lumped resonator and a lumped Purcell filter Transmission line modeled as 50 Ohm resistor Xmon qubit with a JJ or a SQUID Lumped resonators where the inductance is replaced with a JJ array
TOOLS: TOOLS: QuCAT QuCAT Quantum circuit analyzer tool It s based on Foster Foster theorem theorem: : It provides mode frequencies, mode dissipation, mode anharmonicity, and cross-Kerr Natively, it doesn t support JJ arrays
Qiskit Qiskit Metal and library for designing superconducting quantum chips and device Metal: an open-source framework Ansys: Ansys: A platform for performing electromagnetic simulations of quantum chips. With Q3D it is possible to extract capacitance matrix by performing electrostatic simulation
METHODOLOGY METHODOLOGY Step 1: Step 1: Modification of QuCAT'score code to introduce junction arrays by adjusting the non-linearity value Potential energy of a JJ array 2 2? 1 ??,??? ??,??= ? = ?2??,??cos ? ???? ??,?? 4!?2??,??? 4-th order non-linearity of an array of N junctions 4 ???
METHODOLOGY METHODOLOGY Step 2: Step 2: Search for capacitance and inductance values that satisfy the following constraints by using an optimizer ? 1 DISPERSIVE REGIME HARMONIC CONDITION FOR THE RESONATOR ??????? ?? ? ?? BEST CONDITION IN TERMS OF SNR 1 = ?? ??,??? ?? ??,???
METHODOLOGY METHODOLOGY Step 3: Step 3: Design the circuit by using QiskitMetal Step 4: Step 4: Extract the capacitance matrix using Ansys Q3D and calculate the characteristic parameters with QuCAT Step 5: Step 5: Repeat step 3 and step 4 until the desired values are reached
CURRENT STATUS CURRENT STATUS A test chip is designed in collaboration with a PhD student in Chalmers The test chip includes 4 structures with similar parameters Test chip is in fabrication
ALTERNATIVE ARCHITECTURE: ALTERNATIVE ARCHITECTURE: Notch Purcell Filter with JJs ?? and ?? implemented with JJ arrays REQUIRE TUNING OF Lf !! ?? is sized such that Z(??)=0 ?? Qubit mode ??= ??> ?? 2 ?? ??2 1 1 = ?? ??
Design example Cj=75.7 fF Lj=6.4 nH Cr=114 fF Lr=8.5 nH (10 JJs of 0.85nH each) Cg=19.8 fF Cz=17.4 fF Lf=14.5 nH (5 JJs of 2.9nH each) T1= 18.8 ??
Summary Design methodology of lumped element Purcell filters with JJ arrays First prototype under fabrication Alternative architecture
