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CMOS-based cryogenic control of silicon quantum circuits
Xiao Xue, Bishnu Patra, Jeroen P. G. van Dijk, Nodar Samkharadze, Sushil Subramanian, Andrea Corna, Charles Jeon, Farhana Sheikh, Esdras Juarez-Hernandez, Brando Perez Esparza, Huzaifa Rampurawala, Brent Carlton, Surej Ravikumar, Carlos Nieva, Sungwon Kim, Hyung-Jin Lee, Amir Sammak, Giordano Scappucci, Menno Veldhorst, Fabio Sebastiano, Masoud Babaie, Stefano Pellerano, Edoardo Charbon, Lieven M. K. Vandersypen
TL;DR
The paper examines cryogenic quantum-control experiments and describes FPGA-programmed control and readout procedures for silicon spin qubits. It reports decay and finite visibility in two-qubit experiments, attributed largely to residual exchange coupling and charge noise.
Problem
Two-qubit cryogenic control is evaluated under experimental conditions where residual exchange coupling and charge noise affect observed dynamics.
Method
An FPGA configures the cryo-controller and its memories, while spin-selective tunneling with charge sensing provides qubit readout.
Results
Two-qubit experiments show decays in controlled-rotation Rabi oscillations and finite Deutsch-Josza algorithm visibilities.
Takeaways & Limitations
Cryogenic two-qubit control experiments exhibit measurable performance effects associated with coupling and charge noise.
Takeaways & Limitations
Controlled-rotation Rabi decays and finite Deutsch-Josza visibility are largely attributed to charge noise, with greater sensitivity when exchange coupling is enabled.
Abstract
from arXiv · showhide
The most promising quantum algorithms require quantum processors hosting millions of quantum bits when targeting practical applications. A major challenge towards large-scale quantum computation is the interconnect complexity. In current solid-state qubit implementations, a major bottleneck appears between the quantum chip in a dilution refrigerator and the room temperature electronics. Advanced lithography supports the fabrication of both CMOS control electronics and qubits in silicon. When the electronics are designed to operate at cryogenic temperatures, it can ultimately be integrated with the qubits on the same die or package, overcoming the wiring bottleneck. Here we report a cryogenic CMOS control chip operating at 3K, which outputs tailored microwave bursts to drive silicon quantum bits cooled to 20mK. We first benchmark the control chip and find electrical performance consistent with 99.99% fidelity qubit operations, assuming ideal qubits. Next, we use it to coherently control actual silicon spin qubits and find that the cryogenic control chip achieves the same fidelity as commercial instruments. Furthermore, we highlight the extensive capabilities of the control chip by programming a number of benchmarking protocols as well as the Deutsch-Josza algorithm on a two-qubit quantum processor. These results open up the path towards a fully integrated, scalable silicon-based quantum computer.
METHODS
The methods describe programming the cryo-controller, fabricating and reading out silicon quantum-dot qubits, and applying tomography and error analysis to characterize experiments. Two-qubit limitations are attributed primarily to residual exchange coupling and charge noise.
- Cryo-controller programming: An FPGA configures the cryo-controller and programs its envelope memories, instruction tables and instruction lists.The passage gives FTW as an example of an FPGA-configured parameter.
- Device fabrication: The quantum-dot device uses two AlOx/Al gate layers and a patterned 200 nm Co micro-magnet fabricated on top of the heterostructure.The layers comprise 7 nm AlOx with 20 nm Al, followed by 7 nm AlOx with 70 nm Al and a 200 nm Co film.
- Qubit readout: After each operation sequence, Q2 is measured by spin-selective tunnelling to an electron reservoir, distinguishing spin-up (|1⟩) states.The supplied passage describes the readout scheme but is truncated after the spin-up state label.
- Error sources: Residual exchange coupling causes visible decay and beating in simultaneous Rabi oscillations, while charge noise largely limits controlled-rotation decay and Deutsch–Jozsa visibility.Charge-noise sensitivity increases when exchange coupling is turned on for two-qubit gates.
- Quantum state tomography: Quantum-state tomography projects the qubit onto the (−ẑ, +x̂, −ŷ, +ẑ) axes, with direct spin readout used for the −ẑ projection.The other projections are measured using additional operations, but the supplied passage is truncated before specifying them.