3/29/2024 Sarah Maria Hagen
Written by Sarah Maria Hagen
This is Part 2 of a series about the IQUIST presence at the 2024 APS March Meeting. Read Part 1 here.
Improved qubits popular topic with March Meeting attendees
Among the most crowded sessions of the conference were those dedicated to advances in “hardware” qubit implementations. Here, novel superconducting qubit research by the groups of Illinois Physics Professors Bryan Clark and Angela Kou took center stage. Kou’s experimental group works primarily on novel types of superconducting qubits, while Clark’s theoretical group researches various topics at the intersection of quantum information and condensed matter physics.
A superconducting qubit is an electronic circuit made of superconducting material that exhibits quantum properties like superposition. There are several types of superconducting qubits, including the famous transmon qubit adopted by many big players in the quantum computing industry such as Google, IBM and Rigetti.
Other superconducting qubits are promising because they have some advantages over the popular transmon including high gate fidelities—meaning that qubit operations are more reliable—or long coherence times—meaning that the quantum effects are maintained longer. At the March Meeting, Kou gave an overview of recent research about one such qubit called a fluxonium qubit.
Motivated to improve the measurement process of this qubit, Kou group graduate student Aayam Bista presented “The effects of readout photons on the fluxonium qubit.” “The presentation concludes that a strong measurement of the fluxonium qubit causes degradation in preserving its state,” Bista says. “Furthermore, the degradation seems to depend on its coupling strength to the measurement resonator.”
Beyond updates regarding the fluxonium qubit, graduate student Matthew Thibodeau of the Clark group proposed a novel superconducting qubit architecture – the Floquet fluxonium molecule (FFM). “The FFM is made of two strongly coupled fluxonium qubits, known as the ‘fluxonium molecule.’ However, it has important phenomenological differences [from the fluxonium qubit] due to the source of its enhanced coherence, the so-called Floquet drive,” Thibodeau explained.
“The platform is predicted to be highly error resistant. Reducing qubit error rates, in turn, reduces the computational overhead necessary for quantum error correction. Suppose our qubit proposal can be successfully realized. In that case, it will potentially help speed the development of useful error-corrected quantum computers”, Thibodeau added, justifying the crowded room at the novel qubits session.
Perfecting optical qubit techniques
Of course, superconducting qubits are not the only type of qubit. Photonic qubits leverage the inherent quantum nature of light. This allows for some inherent advantages to photonic qubits: namely, the free space transmission of the quantum states. However, photonic qubits are not without their challenges, which several IQUIST members are working to address.
Photonic qubits can travel through optical fiber. The same fiber is quite reliable for classical information tasks like providing internet service, but the infrastructure needs to be much more refined for quantum information. An intra- and extra-IQUIST collaboration is working on solving one the “most basic physical problems encountered when building quantum networks on real-world optical fibers,” says Jaehoon Choi, who presented the talk “Polarization Mode Dispersion Compensation Towards Improved Polarization Based Quantum Networks.”
Choi, a graduate student in the group of Illinois Physics Professor Virginia (Gina) Lorenz, works on building real-life quantum networks that will connect Champaign-Urbana with other Illinois cities connected by optical fiber including Rantoul and Chicago. “Our work presents a way to overcome the wavelength dependence of polarization drift and distortion in optical fibers,” Choi says. “We do this by identifying a particular property of the fiber called the principal axis of polarization mode dispersion. This helps us implement broader bandwidth quantum networks.”
One of the other major hurdles to using photonic qubits effectively is routing them. Since these qubits are seen as the main go-between in future networks of quantum computers, it is imperative to send them to the proper destination at the proper time without compromising the delicate information they contain. This is why one group led by Illinois Physics Professor Paul Kwiat has devoted itself to tackling this issue.
“Quantum networks with more than two nodes will require solutions for routing quantum information through multiple nodes to its destination with high efficiency. I gave an overview of several recent efforts in the Kwiat group to develop technologies for quantum routing,” says Benjamin Nussbaum, a graduate student who presented the talk “Technologies for quantum routing.”
His fellow group member Ujaan Purakayastha’s talk “Fast Optical Switching for Quantum Information” focused on an element of the same routing problem: an optical switch. “The ability to rapidly route photonic states is key to several applications, including making better single-photon sources, counting photons at higher rates, and overcoming photon loss in certain protocols,” he says.
Purakayastha’s work was successful in changing the path taken by a single photon at timescales of picoseconds (1 picosecond = 1 trillionth of a second). He explains that this was possible by making the photon interact with a strong pulse of light in an optical fiber. However, he notes that there is room for improvement: “The polarizations of the single photon and the co-propagating pulse do not undergo the same transformations as they traverse the optical fiber, and this makes the interaction somewhat inefficient.”
More quantum research to come
Next year’s March Meeting in Anaheim, California will highlight the subject since 2025 has been chosen as the International Year of Quantum, in honor of quantum mechanics’ birth 100 years prior (the term was coined by German physicist Max Born in 1925).
Research presented at next year’s conference and the preparation for the meeting itself is already underway. “From the moment one March Meeting ends, planning for the next one begins,” says Illinois Physics Professor Smitha Vishveshwara, who served in the role of Past Chair at this year’s March Meeting after chairing the 2023 March Meeting in Las Vegas. She emphasizes the exciting presence of quantum science at the conference: “You can see the growth of quantum science at the March Meeting by looking at indicators like the rapid growth of the APS Division of Quantum Information and the huge presence of quantum industry partners in the exhibit hall.”
What does Vishveshwara have to say about next year’s quantum programming? “You can expect something big,” she says laughing.