Behind the Cover: March 2023

Each month, Physics Today editors explore the research and design choices that inspired the latest cover of the magazine.

Quantum information and quantum computing are hot topics in research and in the pages of Physics Today. (For newcomers to the topic, a good place to start is “What’s under the hood of a quantum computer?,” Physics Today online, 5 March 2021 .) Researchers in the field are exploring, among other issues, what types of qubits or combinations of qubit types have the right properties for future technological and research needs. Commercial quantum computers thus far have largely relied on superconducting or trapped-ion qubits (see Physics Today, November 2020, page 22 ).

On page 28 of the March issue , Michael Wasielewski introduces a relatively new qubit contender: molecules that host entangled electron spins. For three linked molecules, a photoexcited electron can travel from a donor molecule across a bridge molecule to an acceptor molecule. The electron leaves behind an electron hole, and the electron and hole form a spin pair, which can take various singlet and triplet spin states. The molecular spin pairs can perform quantum gate operations and be extended to three- and four-spin systems.

The cover art hints at molecules with a photo of a classic ball-and-stick model, which senior graphic designer Freddie Pagani transformed to evoke a superposition of states. First she saturated the colors and separated the red, green, and blue channels. She then layered the channels at different sizes and angles to create a rich, multidimensional look. Pagani chose the Vektra font for the cover line to echo that layering.