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Design of a superconducting qubit coupler with on-demand exponential suppression of virtual interactions

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Quantum computing originated in the 1980s, when it was proposed that a computer based on quantum mechanics could simulate algorithms that a classical supercomputer would be unable to perform in "Universe time". Several decades later, quantum computing is still in its infancy, but it has recently seen a number of important developments around the world. Discoveries in quantum technology are accelerating markedly in the 21st century.

Despite this, quantum processors today remain small-scale and are limited in their applications and benefits. The promise of high-performance quantum computing lies in replacing transistors that encode bits of information with discrete values 0 and 1, with an abstract object called a qubit. The latter can exist in a superstition of the two values 0 and 1. Moreover, it is possible to entangle two qubits, so that the probability of measuring 0 or 1 in the first qubit depends on the state of the second. This is what causes the exponential gain in performance of a quantum computer, from a theoretical point of view.

The qubit can be implemented in different physical systems governed by quantum mechanics. One of these systems is the superconducting circuit, object of the present invention.


This invention is a new type of coupler between two qubits, more precise than any other proposed today. This technology is, among other things, an answer to the question: how to improve future generations of large-scale quantum processors. The ultimate goal is to perform fast, high-fidelity quantum computations. The technology of this invention is based on a new physical mechanism for couplers, the so-called delocalization of the calculation states of the coupler, in the space of the auxiliary systems, here resonators. The novelty appears when it is desired not to activate any operation between the qubits, by manipulating their components, which makes it possible to exponentially eliminate any unwanted residual interaction between them. In general, qubits are very difficult to control, and this invention makes it possible to improve this control, and therefore to increase the reliability of quantum calculations. This device allows the control of many qubits, which is fundamental for the high-fidelity operation of these devices.

This "quantum switch" allows to attenuate the parasitic interactions between many qubits, called "crosstalk". These undesirable interactions are very detrimental to the computational fidelity of a processor and, in particular, to the quantum error correction. For these reasons, this technology could become a high-fidelity quantum computing tool and therefore a key element of superconducting quantum processors.

We present a novel superconducting-qubit coupler design exhibiting an exponentially large on-off ratio that is controlled by the amplitudes of the microwave commands. We demonstrate how this scheme can be used to reduce residual cross-Kerr interactions by several orders of magnitude in transmon-qubit-based quantum processors. Finally, we present an implementation of the superconducting circuit device, which can simultaneously enable two-qubit parametric gates and help reduce crosstalk.


  • A totally unique solution for a coupler or a switch:

    • There is no need for fine tuning of parameters in this system.

    • The coupler is expandable to a processor

    • It can be used in conjunction with other solutions currently under study.

  • Coupler (switch) that can exponentially remove the interaction between 2 qubits:

    • Occurs fairly quickly and on demand, meaning the interaction can be turned on and off quickly to set up or prevent 2-qubit gates as needed

    • The "off" state of the switch is noise-resistant, which is ensured by the exponential suppression of interactions, making this technology unique and far superior to previous coupler approaches

  • Competitive advantage over comparable technologies on the market:

    • A high-quality, large-scale quantum processor that is very difficult to achieve.

    • Scalable cutting-edge superconducting technology for quantum computing

    • A new physical mechanism for couplers

    • Can be used in conjunction with other error removal techniques

    • Could improve the fidelity of long and complex quantum algorithms

    • Could improve the performance of any technology that requires a switch

    • Compared to other technologies:

    • Does not require fine tuning 

    • Exponential reduction in noise sensitivity

    • Exponential reduction of ZZ error

    • Exponential reduction of information offshoring

    • Exponential Crosstalk Reduction

    • Quick Device Check

  • New implementation of a strong cross-Kerr interaction in superconducting circuits, also useful in other contexts.

  • Once the device is manufactured, the architecture of the invention is designed to be compatible with the processors already built today.


  • Quantum computers - a component of the superconducting processor.

  • A growing market - Markets & Markets 

    • The quantum computer market is expected to reach US$1.8 billion by 2026.

    • Early adoption in the banking and financial sectors is expected to fuel the growth of the global market. Other growth factors are:

    • Increased investment by national governments to conduct R&D activities related to quantum computing technology.

    • Several companies are focusing on QCaaS (Quantum Computing as a Service).

    • Superconducting qubits take the top spot by type of quantum processor technology – estimated $966 million by 2026. 



  • TRL 2-3

  • Theoretical development completed:

  • Proof of concept device under development in a partner institution. 

  • The first version is imminent 

  • It will be followed by several refinement iterations. 

  • A satisfactory proof of concept is expected within 3 years, which will bring the technology to TRL 4-5.


  • Patent pending in the United States.



Project Director: François Nadeau

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