Radio frequency (RF) components and cables are used in quantum computing to transmit signals that manipulate the state of qubits, the basic unit of quantum computing. These components are typically operated inside a dilution refrigerator with temperatures as low as tens of milli-kelvin (mK). The RF performance of these components can be characterised by measuring their scattering parameters, known as S-parameters, which describe how energy propagates through an electrical network. S-parameters describe the relationship between different ports of the electrical network at RF frequencies when it is important to describe the network in terms of the amplitude and phase change of the transmitted and reflected signals as a function of frequency, rather than the voltage and current representation used at lower frequencies. The S-parameters can be utilised to extract other useful information such as the electrical properties of transmission lines, equivalent circuit models, material properties, crosstalk and losses.
Accurate determination of S-parameters in a cryogenic environment benefits quantum computing by supporting the development of active and passive cryo-electronic devices, cables and interconnects, multiplexers, quantum and RF integrated circuits, flux quantum electronics, cryo-CMOS technologies, quantum hardware packaging, small-signal and waveform metrology, and parametric amplifier development. In addition to quantum computing, scientific applications requiring accurate S-parameter characterisation at low temperatures include radio astronomy and high frequency electronic transport experiments.
Typical RF components in a quantum computer
The cryogenic device S-parameter measurements are usually adversely affected by the cables and other components inside the dilution refrigerator, which need to be “corrected” using calibration techniques to gain a better understanding of the device behaviour. NPL specialises in performing calibrated S-parameter measurements at cryogenic temperatures, as low as tens of mK, using an NPL-developed cryogenic RF calibration unit.
Read our work on characterising quantum integrated circuits at milli-kelvin temperatures.
Read our work on characterising RF integrated circuits at milli-kelvin temperatures.
Watch this video characterisation of quantum and RF components at milli-kelvin temperatures.
Our expertise and capabilities offer solutions suitable for both industrial applications and fundamental research. We can provide:
- Support with development of new and improved cryogenic RF components and systems by characterising them at frequencies up to at least 18 GHz and at temperatures down to at least 15 mK
- Passive coaxial components such as cables, interconnects, packaged quantum devices, filters, attenuators, etc.
- Active coaxial components such as LNAs, parametric amplifiers, mixers, etc.
- Multi-port coaxial components such as multi-qubit circuits, switches, multiplexers, circulators, etc.
- RF and quantum integrated circuits such as qubits, resonators, cryo-electronics, attenuators, etc.
- Support with the development of RF installations in dilution refrigerators by characterising the RF performance of coaxial lines and new RF interfaces at frequencies up to at least 18 GHz at various temperature stages.
We are also actively involved in a wide range of collaborative research projects such as Altnaharra and EPIQC, and investigations into innovative test applications and processes involving cryogenic measurements is ongoing through the National Quantum Technologies Programme.
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