Developed by a group of researchers at the National Institute of Standards and Technology (NIST), this quantum computer device features a pair of superconducting quantum bits, known as qubits, serving as the quantum computer’s equivalent of classical computer processing chip’s logic bits.
At the core of this innovative approach lies a “toggle switch” mechanism, connecting the qubits to a circuit called a “readout resonator.” This resonator plays a crucial role in deciphering the qubits’ computational results.
The toggle switch within this system offers the ability to adjust the strength of connections between the qubits and the readout resonator by toggling it into different states. In the “off” state, all three components are effectively isolated.
However, when the switch is toggled “on,” facilitating a connection between the two qubits, they can interact and execute computations. After completing the calculations, the toggle switch can connect either of the qubits and the readout resonator, enabling the retrieval of results.
Including a programmable toggle switch significantly mitigates noise, a prevalent issue in quantum computer circuits that often hampers the qubits’ computational performance and result accuracy. Qubits can perform calculations more effectively and exhibit more precise output with reduced noise.
Ray Simmonds, a physicist at NIST, explained the objective as ensuring the undisturbed functioning of the qubits during calculations while allowing for their readout as needed. He stated, “The goal is to keep the qubits happy so they can calculate without distractions while still being able to read them out when we want to.”
The device architecture employed in this study not only safeguards the qubits but also holds the potential to enhance our capability to perform high-fidelity measurements, which are crucial for the development of quantum information processors utilising qubits.
Quantum computers, which are currently in an early stage of advancement, utilise the unusual characteristics of quantum mechanics to tackle highly challenging tasks for our most advanced classical computers. These tasks include facilitating the creation of new pharmaceuticals through intricate simulations of chemical interactions.
Nevertheless, designers of quantum computers still face numerous challenges, such as quantum circuits are susceptible to external or internal noise, which originates from imperfections in the materials employed to construct the computers. This noise, characterised by random behaviour, has the potential to introduce errors in the calculations performed by qubits.
The team’s programmable toggle switch addresses two issues. Firstly, it prevents circuit noise from entering the system through the readout resonator and ensures that the qubits remain silent when necessary, reducing a significant noise source in quantum computers.
Secondly, it controls the opening and closing of switches between elements using small microwave pulses, enabling a more flexible and programmable quantum computer. With multiple toggle switches, the chip’s functionality can be modified through software, offering greater versatility. Additionally, the toggle switch allows simultaneous measurement of both qubits, facilitating error detection in quantum computations.
In this demonstration, the qubits, toggle switch, and readout circuit were constructed using superconducting materials that allow electricity flow without resistance and require shallow operating temperatures. The toggle switch is composed of a superconducting quantum interference device (SQUID), exhibiting high sensitivity to magnetic fields passing through its loop. By driving a microwave current through a nearby antenna loop, interactions between the qubits and the readout resonator can be induced when necessary.
The team has only worked with two qubits and a single readout resonator. However, they are preparing a design that involves three qubits and a readout resonator, with plans to incorporate more qubits and resonators in the future.
Further exploration in this area of research may provide insights into how to connect multiple devices, potentially leading to the development of a powerful quantum computer with a sufficient number of qubits capable of solving currently intractable problems.
