A Wideband Low-Power Cryogenic CMOS Circulator for Quantum Applications

Quantum computers require classical electronics to ensure fault-tolerant operation. To address compactness and scalability, it was proposed to implement such electronics as integrated circuits operating at cryogenic temperatures close to those at which quantum bits (qubits) operate. Circulators are among the most common blocks used in the qubit readout chain, but they are currently discrete devices with a bulky footprint, thus preventing large-scale system integration. For this reason, we present here a detailed description of the first fully integrated CMOS circulator operating from 300 K down to 4.2 K to be an integral part of cryogenic quantum computing platforms. At 300 K, the circuit's operating frequency is centered around 6.5 GHz with 28% fractional bandwidth, and it has 2.2-dB insertion loss, 2.4-dB noise figure, and 18-dB isolation while consuming 2.5-mW core power. These results are achieved thanks to a fully passive architecture based on $LC$ all-pass filters, which allows achieving a $1.6\times$ increase in fractional bandwidth and the lowest power consumption with respect to the state of the art while using only 0.45 mm(2) of core area. This allows miniaturization of circulators in power-constrained multi-qubit readout systems.

A cryo-CMOS chip that integrates silicon quantum dots and multiplexed dispersive readout electronics

Edoardo Charbon, Yatao Peng, Andrea Ruffino

An integrated circuit fabricated using industry-standard 40 nm complementary metal-oxide-semiconductor technology can combine silicon quantum devices, digital addressing and analogue multiplexed dispersive readout electronics. As quantum computers grow in complexity, the technology will have to evolve from large distributed systems to compact integrated solutions. Spin qubits in silicon quantum dots are thought to offer good scalability because both spin-carrying quantum dots and support complementary metal-oxide-semiconductor (CMOS) electronics can, in principle, be monolithically integrated on a single chip. However, monolithically integrated quantum-classical hybrid circuits based on industry-standard CMOS technology remain limited. Here we report a millikelvin integrated circuit fabricated using 40 nm CMOS technology that integrates silicon quantum-dot arrays with support electronics in an architecture that allows the array to be efficiently addressed and read. The architecture contains integrated microwave lumped-element resonators for dispersive sensing of the charge state of the quantum dots, mediated via digital transistors in a column-row-addressing distribution. With the chip, we demonstrate combined time- and frequency-division multiplexing, which scales sublinearly the resources as well as footprint required for readout.

NATURE PORTFOLIO2021

Towards a scalable quantum computer

Edoardo Charbon, Fabio Sebastiano

A quantum machine may solve some complex problems that are intractable for even the most powerful classical computers. By exploiting quantum superposition and entanglement phenomena, quantum algorithms can achieve from polynomial to exponential speed up when compared to their best classical counterparts. A quantum computer will be a part of a heterogeneous, multi-core computer in which a classical processor will interact with several accelerators such as FPGAs, GPUs and also a quantum co-processor. Figure 1 shows the different layers of the quantum computer system stack [1]. Building such a quantum system requires contributions from different fields such as physics, electronics, computer science and computer engineering for addressing the following challenges: i) build scalable quantum chips integrating qubits with long coherence times and high-fidelity operations, ii) develop classical control electronics at possibly cryogenic temperatures and iii) create the microarchitecture as well as the software for quantum computation.

2018

Cryo-CMOS Circuits and Systems for Quantum Computing Applications

Edoardo Charbon, Harald Arjan Robert Homulle, Fabio Sebastiano

A fault-tolerant quantum computer with millions of quantum bits (qubits) requires massive yet very precise control electronics for the manipulation and readout of individual qubits. CMOS operating at cryogenic temperatures down to 4 K (cryo-CMOS) allows for closer system integration, thus promising a scalable solution to enable future quantum computers. In this paper, a cryogenic control system is proposed, along with the required specifications, for the interface of the classical electronics with the quantum processor. To prove the advantages of such a system, the functionality of key circuit blocks is experimentally demonstrated. The characteristic properties of cryo-CMOS are exploited to design a noise-canceling low-noise amplifier for spin-qubit RF-reflectometry readout and a class-F2,3 digitally controlled oscillator required to manipulate the state of qubits.

2017