Luminescent organic molecules for quantum information science

• A team including an Oxford chemist report a highly-sought molecular spin-optical interface for quantum information science.
• Microwave pulses can be used to control the luminescence of the specially designed molecule in its excited high-spin state.
• The study, published this week in the journal Nature, shows that quantum state preparation, manipulation, and read-out are possible in this specially-designed molecule at room temperature.

In the world of quantum information science, nitrogen-vacancy defects in diamond are well-known as an example system in which the user can “read out” the information encoded in its spin state. This “read out” process can be thought of as similar to the way that a conventional computer must be able to read the ones and zeroes encoded in silicon chips in order to function.

Diamond vacancies work so well for this because they will luminesce after absorbing a photon, which means that researchers can probe their spin states using pulses of light. Certain organic molecules exhibit very long-lived spin states, which would be of great interest for quantum information science. However, to date the difficulty has been finding such molecular systems that would luminesce like diamond does and allow us to easily “read out” the information encoded in the spin state.

Now, based on a strong background in preparations of molecules for optoelectronic applications, the team behind a study published today in Nature have designed a molecule that shows an almost perfect yield of light-generated excited states (those with spin multiplicity S > 1) that can then be controlled using microwave pulses and read out by emission of optical photons. The molecules contain an energy matching property of Thermally Activated Delayed Fluorescence (TADF) that is useful both in preparation of the excited state and its luminescence.

Figure 1: Cartoon representations of the photogeneration sequence of the excited state (a trip-quartet state 4[D0T1]), radical-chromophore molecule and a two-dimensional measurement of electron spin echoes at 20 K, after laser flash.

The international team involved in the work brings together talented researchers from UK universities in Oxford, Cambridge, Manchester, and Swansea, as well as colleagues in Belgium, Germany, Spain, and China. The team combined synthesis, optical, and electron spin resonance (ESR) characterisation, along with theoretical methods modelling the excited states involved.

Figure 2: The Centre for Advanced ESR, located on the first floor of the Inorganic Chemistry Laboratory.

Design and synthesis of chemically tuned systems like these will allow new opportunities to make molecules whose states can be both formed and interrogated with optical photons, whilst being driven in excited state transformations by microwave photons.

You can read more about the study in the Nature article here.

Images: Will Myers.