Standards Development

Scope

The proposed activity includes:

- Identification and definition of the key parameters and quantities of interest for cabling components used in control / measurement highways, in view of accommodating the needs and requirements of quantum technologies applications at low temperature, whether in the DC or RF domain. These cabling components includes cables, connectors and other connection solutions integrating further functionalities (filters, attenuators…).

- Define the different methods for measuring these parameters and quantities, and their suitability to the cryogenic vacuum environment. This makes it possible to identify a reference methodology for measuring each parameter.

- Identification of the tools and equipment needed to measure these parameters and quantities (refrigerators, VNA, thermometers, etc.).

- Data analysis, to some extent.

At the time of writing, the identified parameters of interest include but are not limited to:

1. Reverse gain, insertion loss or transmission phase (i.e. S12) [dB] vs frequency [Hz] vs temperature [K],

2. Forward gain, insertion loss or transmission phase (i.e. S21) [dB] vs frequency [Hz] vs temperature [K],

3. Input reflection coefficient, return loss, VSWR (i.e. S11) [dB] vs frequency [Hz] vs temperature [K],

4. Output reflection coefficient, return loss, VSWR (i.e. S22) [dB] vs frequency [Hz] vs temperature [K],

5. Impedance [Ohm] vs temperature [K],

6. Operating frequencies bandwith [Hz],

7. Linear capacitance [pF/m],

8. Thermal resistance [K/W] and conductance [W/K]

9. Operating temperature [K]

10. Dimensions, shape and associated tolerance [mm]

11. Stabilization time [ms] after thermalization (e.g. after DC or RF pulse)

12. Screening effectiveness [dB] vs frequency [Hz]

13. Crosstalk [dB] vs frequency [Hz]

14. Ageing: RF performance conservation (1, 2, 3, 4, 12, 13) after [nb] of temperature cycling

Mechanical robustness againstvibrations and mechanical stress (under vacuum, at low temperature),immunity against magnetic field, IR and thermal radiation could also be considered if needed.

The work item does not aim at specifying numerical values of the parameters of interest because they will depend on quantum technologies used.

Purpose

Cables and connectors, whether RF or DC, is omnipresent in the world around us, as it enables systems to be interconnected. To date, most of the market has concentrated on applications at ambient temperature, or at temperature in a range relatively small compared with the possibilities. Thus, it is only natural that the existing parameters and measurement methods for RF and DC cables and connection components suit these usual conditions. However, the field of quantum technologies, whose market has been growing steadily in recent years, involves extremely low temperatures (down to 10mK) which override the usual considerations. To date, Quantum Processing Units (QPUs) manufacturers have adapted to the current worldwide RF & DC lines offer, which consists, for example of superconducting cables already used in other fields (research, aerospace, medical, industry, etc.) and specified for higher operation temperature, and have reused these solutions for quantum technologies. Unfortunately, claimed performances are too often unreliable, as they are measured using methods unsuitable at low temperature or in higher temperature regime. This is completely at odds with the demands of quantum technologies, where the slightest external disturbance can destroy a quantum state. Instead, we would need to master every aspect of these new systems. This includes RF & DC lines, from external room temperature control or measuring units, down to the components placed at ultra-low temperature (e.g., 10 mK), where lies the experiment or quantum processing unit operation.Knowledge of the electrical, mechanical and thermal properties of quantum-compliant wiring or so-called control / measurement highways, in the RF domain, over a whole frequency range up to 20 GHz, and at potential end-use temperatures down to 10mK, would be a major advantage for system integrators, enabling them to better identify solutions adapted to their needs. The use of standardized measurement methods for identified parameters of interest, will give end-users greater confidence in the performances given by manufacturers, while enabling them to make genuine comparisons between several products, whether they come from the same or several Licensed to: Siddons, Aymee Ms Downloaded: 2024-09-25 Single user licence only, copying and networking prohibited Page 2 of 7 suppliers. Another major advantage of standardizing these methods is to offer integrators FFF (Fit, Form and Factor) products, enabling them to secure their supply chain. So, suppliers of RF & DC lines will support system integratorsthanks to this standardization approach. This could involve redefining/adapting existing measurement methods for these new environments. It would also need the use of more specific tools and equipment. The objective of guaranteeing appropriate parameters and test methods for RF & DC lines at low temperature for quantum technologiesis crucial to the successful and reliable operation of quantumsystem. This is evenmore important with the scaling up of the number of qubits soon. This scaling up will require new products such as high-density coaxial cable harnesses with integrating functionalities asfilters, attenuators or infrared blocker; multiport and well-thermalized connector assembly; all being able to accommodate manyRF lines (potentially several hundreds) in a limited footprint. To date, there are no characterization methods for these new products. How to characterize, for example, a matrix of 10x10 coaxial cables and associated connectors and components at low temperature? Would individual characterizations be more appropriate? If so, which tool(s)/instrument(s) should be used? The purpose of this document is to provide answers to these questions