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HomeSciencePhysicsMeet the Unimon, the New Qubit on the Block

Meet the Unimon, the New Qubit on the Block

• Physics 15, 191

In preliminary exams, a simplified model of a preferred superconducting qubit achieves excessive computation accuracies, making it engaging for future quantum computer systems.

IQM Quantum Computers

A microscope image shows a silicon chip containing three unimon qubits (blue). The “drive lines” (green) provide pathways for microwave pulses to switch the change of any unimon and so carry out logical steps. Resonators (red) allow reading out the states of the qubits.A microscope image shows a silicon chip containing three unimon qubits (blue). The “drive lines” (green) provide pathways for microwave pulses to switch the change of any unimon and so carry out logical steps. Resonators (red) allow reading out the s… Show more

Physicists creating quantum computer systems have more and more turned to a superconducting aspect known as the transmon to retailer quantum info and shield it from noise. Now researchers have demonstrated a associated circuit aspect, the unimon, which they are saying is much less liable to disruption by noise [1]. With additional growth, the workforce behind the unimon thinks that it could possibly be used to construct quantum computing methods with larger computing accuracy than people who use transmons.

A key problem in making a quantum laptop is defending the delicate computing parts from environmental noise, which might trigger errors in computations. The most correct transmon—a preferred superconducting qubit—at the moment achieves accuracies of between 99.98 and 99.99% for a single computing step (one transmon performing one logical operation). Although this accuracy appears spectacular, a hypothetical gadget containing 100 transmons and working calculations with ten computing steps would solely have a 50% probability of yielding an accurate end result, says Mikko Möttönen of Aalto University, Finland, and IQM Quantum Computers, the corporate behind the unimon. Future quantum computer systems will doubtless include much more qubits and their computations many extra steps, and so will carry out a lot worse.

Some quantum computing strategies can partially right such errors. Even so, researchers agree on the necessity to increase the accuracy of single-step computations properly past 99.99%. To accomplish that, Möttönen and colleagues designed what they are saying is a “surprisingly simple” qubit, which they name the unimon.

Transmons are constructed from superconducting circuits and key parts known as Josephson junctions, with capacitors and different parts additionally included to cut back sensitivity to noise. Like any qubit aspect, a transmon can tackle a number of totally different quantum states. Researchers typically use the bottom two states to retailer quantum info. They then shift transmons from one state to a different utilizing a microwave photon pulse that has a frequency matching the vitality distinction between the states, that are equally spaced relative to at least one one other.

This equal spacing, recognized an harmonicity, is behind a key limitation of present transmons, because it means they’ll simply be excited into states not used for quantum computing. For instance, if a transmon absorbs two photons quite than the traditional one, it is going to transfer right into a state above the 2 used for info storage, inducing an error. Harmonicity additionally limits computing pace as a result of utilizing shorter microwave pulses, which make computations faster, makes errors extra doubtless.

For these causes, Möttönen and colleagues sought to create a superconducting qubit with a excessive anharmonicity—unequally spaced vitality ranges. In the method, in addition they streamlined its construction. “When we started, we wanted a very simple circuit, as it’s easier to build larger computing systems using simple elements,” Möttönen says. Ultimately, the workforce selected a design with a single Josephson junction positioned inside a superconducting resonator. The gadget is “the simplest device we could come up [with] that might act like a good qubit,” he provides.

In a collection of exams on three totally different unimon units, the workforce discovered single-step computing accuracies of round 99.9%, not far beneath the present accuracy of the perfect transmon methods. As a end result, they count on the unimon to take a major place in ongoing computing analysis. “The fact that the very first unimon[s] ever made work so well gives plenty of room for further optimization,” Möttönen says.

The unimon “is an important new qubit” within the superconducting quantum computing toolbox, says electrical and laptop engineer Thomas Roth of Purdue University in Indiana. “In addition to the larger anharmonicity, this qubit should be easy to manufacture and should allow designers many options for optimization that were not possible with earlier qubit designs.”

The subsequent step for the workforce, Möttönen says, is to display comparable accuracies in additional difficult two-unimon-qubit circuits, which can be required in constructing as much as extra advanced computing methods. The group additionally hopes to optimize the design to attain accuracies past 99.99%.

–Mark Buchanan

Mark Buchanan is a contract science author who splits his time between Abergavenny, UK, and Notre Dame de Courson, France.


  1. E. Hyyppä et al., “Unimon qubit,” Nat. Commun. 13, 6895 (2022).

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