Quantum Computing

Scalable Quantum Control and Readout System

Team Members: Ujjawal Singhal, Shantharam Kalipatnapu, Pradeep Kumar Gautam, Sourav Majumder, Vaibhav Venkata Lakshmi Pabbisetty, Srivatsava Jandhyala, Vibhor Singh, Chetan Singh Thakur

Quantum computers can solve certain computational problems much faster than ordinary computers by using specific quantum properties. The basic building blocks of such machines are called quantum-bits or qubits. Qubits can be realised using several physical platforms, such as nuclear spins, trapped ions, cold atoms, photons, and superconducting Josephson circuits. Several such qubits operate in the microwave frequency domain and require specialised room-temperature microwave electronics for control and readout of the quantum states of the qubits.

However, there lies a challenge when it comes to connecting classical electronics to these qubits. The qubits need high-frequency (GHz) electromagnetic signals for control and readout pulses in the order of a few tens of nanoseconds. The traditional setup for generation and capture of such signals is often costly and complex with many components. This can be addressed by developing a specific FPGA-based system that brings the functionality of all the traditional equipment onto a single board. However, with such developments, three main challenges need to be kept in mind: generation and capture of the high-fidelity microwave signals, scalability, and a user-friendly interface.

Figure : System Architecture of 4-Qubit SQ-CARS

We have addressed these challenges with the development of a Scalable Quantum Control and Readout System (SQ-CARS), using Xilinx RFSoC FPGA board. SQ-CARS is designed to be scalable, configurable, and phase-synchronized, providing multiqubit control and readout capabilities. The system offers an interactive Python framework, making it user-friendly. Scalability to a larger number of qubits is achieved by deterministic synchronization of multiple channels. The system supports direct synthesis of arbitrary vector microwave pulses using the second Nyquist zone technique, from 4 to 9 GHz. It also features onboard data processing such as tunable low-pass filters and configurable rotation blocks, enabling lock-in detection and low-latency active feedback for quantum experiments. All control and readout features are accessible through an onboard Python framework. Our team tested their SQ-CARS system by conducting different experiments with superconducting transmon qubits and benchmarking it against the traditional setup.

Ref: Ujjawal Singhal, Shantharam Kalipatnapu, Pradeep Kumar Gautam, Sourav Majumder, Vaibhav Venkata Lakshmi Pabbisetty, Srivatsava Jandhyala, Vibhor Singh, Chetan Singh Thakur, “SQ-CARS: A Scalable Quantum Control and Readout System,” IEEE Transactions on Instrumentation and Measurement, Vol. 72, 2023. DOI: https://doi.org/10.1109/TIM.2023.3305656.