Controlling
the orientation of a single unpaired electron (called its spin) is no easy
task, especially if the electron is in a molecule in its lowest energy state.
Yet the ability to control the orientation of the electrons is important to the
development of some quantum computing strategies. In this research, scientists
show that in a magnetic field, visible light can be used to influence a
relative orientation of an unpaired electron in a molecule. When the molecule
absorbs light, other electrons in the molecule are excited and become unpaired.
The unpaired spins interact with each other, influencing how the electron spins
recombine as the molecule relaxes. These interactions orient the remaining spin
parallel or antiparallel to the direction of an applied magnetic field.
To
process information, some quantum computing strategies will rely on
manipulation of the spin of electrons. However, it is challenging to control
electrons’ spins. This research identifies a strategy to influence the relative
orientation of a spin that can be applied across a class of small molecules.
This process “prepares” the spin for further manipulations required in the
longer-term for technological applications. This research takes a step toward
these novel technologies by helping scientists control the properties of
unpaired electrons through molecular design.
This
study establishes a new strategy to control the orientation of an unpaired spin
in a molecule in its lowest energy state (i.e., its ground state). An unusual
feature of this approach is that the researchers believe it can be
generalizable across a class of small molecules. These small molecules are
designed to enter short-lived excited states that last less than a billionth of
a second when they absorb light, even at very low temperatures of approximately
20 Kelvin. The short lifetimes of these excited states, in concert with
designed molecular features, determine the properties of the unpaired electron
during the lifetime of the excited state and transmit those properties to the resulting
“ground” state. As a result, the approach can dramatically enhance the
detectable features of the unpaired electron, and the sign of the signal can be
reversed in less than a billionth of a second simply by exposing the molecules
to visible light. Such a response holds promise for future quantum computing
and quantum-based sensors, which may rely on spin control to advance quantum
information science.
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