A novel oppositely anharmonic coupler for quantum computer gates
ISSUE ADDRESSED
Quantum computing has recently seen a number of significant successes around the world. As a result, several governments across the globe have implemented national quantum strategies in recent years to encourage research and development in this area. Still in line with this growing interest, the quantum computing market is experiencing annual growth of 30%!
By exploiting the intrinsic properties of quantum mechanics, quantum computers will bring exponential improvements to solve problems that classical computers can never solve. Quantum technologies will have a positive impact on several economic sectors, such as aerospace, communications, energy and pharmaceuticals.
The quantum bit, or 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.
TECHNOLOGY
This invention is the result of a collaboration between Princeton University and the University of Sherbrooke in Canada. This is a new device intended to be used as a coupler between two qubits, which is an improvement over existing couplers for quantum computers.
Current technologies require multiple coupling elements and close-frequency qubits to suppress crosstalk in two-qubit gates. This leads to frequency congestion and reduces the efficiency of useful devices. Technology exists to suppress crosstalk between tunable qubits, but these tunable qubits have lower coherence times than fixed-frequency qubits.
Strong qubit-qubit interactions are crucial for the realization of a scalable quantum computer. Currently, the performance of high-coherence "transmons" is limited by unwanted Kerr crosstalk or "ZZ". The use of interference between two couplers has already made it possible to attenuate ZZ crosstalk. Here we propose a novel tunable coupler design that exploits the interference due to higher energy levels to achieve zero static ZZ coupling between the two qubits. By focusing on the null ZZ interaction, we achieve fast perfect entanglement with parametric flux modulation in less than 20 ns. This coupler provides very fast gates between far-detuned fixed-frequency qubits and is a crucial part of large-scale quantum computers.
This solution makes it possible to attenuate the problems of frequency congestion and coherence. Moreover, by systematic design, we can achieve perfect 18 ns tangles, which represents a speed increase of more than 5 times in such systems. This will increase the depth of circuits achievable in superconducting quantum processors, i.e. the number of gates that can be executed before the system becomes overwhelmed with errors, or “decohesives”.
ADVANTAGES
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Ability to achieve fast, high-fidelity entanglement gates – an important requirement for a viable quantum processor.
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The inventors have experimentally demonstrated that an entanglement gate can be made in less than 20 ns.
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A new type of coupler - the most faithful gate of any system, commercial or academic.
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An improvement over the couplers of current commercial quantum computers.
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This combined analytical and numerical strategy enables characterization of two-qubit gates involving parametric interactions and can be applied to gate optimization and crosstalk mitigation, such as cancellation of unwanted ZZ interactions in multi- qubits.
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True 0 crosstalk without the need for multiple coupling objects.
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Fixed frequency qubits that can preserve long coherence.
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A wide range of coupler designs are possible.
APPLICATIONS
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Quantum computers:
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A superconducting processor component.
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This invention can be used to improve the commercial quantum computers that exist today.
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A growing market (Markets & Markets):
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The quantum computing market was valued at US$328 million in 2020 and is expected to reach US$1.8 billion by 2026, growing over 30% annually!
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Early adoption in the banking and financial sectors is expected to fuel the growth of the market globally. Other growth factors are:
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Increased investment by national governments to conduct R&D activities related to quantum computing technology.
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Several companies are focusing on QCaaS (Quantum Computing as a Service).
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Superconducting qubits take the top spot by type of quantum processor technology – estimated $966 million by 2026.
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INTELLECTUAL PROPERTY STATUS
TECHNOLOGY MATURITY
TRL 3-4
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The inventors of the two universities verify the properties of the circuit by numerical simulations and experimental constructions.
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The proof of concept exists; several devices have been built.
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The University of Sherbrooke carries out the theoretical work and the University of Princeton the experimental verification.
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Measurements are made on the devices and an iterative cycle ensues.
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At least 3 devices have been built to date.
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More details are available here: https://arxiv.org/abs/2107.02343
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Developments are continuing in order to optimize the solution and verify reproducibility.
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INTELLECTUAL PROPERTY
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Filing of a PCT international patent application.