When String Theory Influences Quantum Simulations

Theoretical physicists routinely introduce fictitious particles and fields into their calculations either to complete a theory or simply to make it more concise. A striking example concerns the magnetic monopole imagined by Dirac in 1931. This is a point-like source of magnetic field that does not exist in classical electromagnetism. Dirac monopoles have not been observed in nature, but appear artificially in various physical settings, especially in the solid state.

In 2018, Giandomenico Palumbo and Nathan Goldman (Faculty of Science, ULB) proposed an experimental scheme in which the exotic ‘tensor’ monopoles, first introduced in string theory, could be created and observed in the laboratory. These tensor monopoles are point-like sources of generalized magnetic fields (known as Kalb-Ramond fields) that exist in four-dimensional space and appear naturally in the mathematical framework of string theory.Palumbo-Goldman core results published in physical review letter In 2018, it was revealed that tensor monopoles can be artificially created by manipulating simple quantum systems such as laser-coupled three-level atoms.

In the new issue at chemistry, Paola Cappellaro (MIT) and her team describe an experimental implementation of the Palumbo-Goldman model, and the associated observations and characterization of tensor monopoles. In this experiment, the team manipulates artificial atoms enabled by diamond defects (nitrogen vacancy centers or NV centers). Using this highly controllable quantum setup, the experimenter prepared a synthetic monopole, measured her radiating Kalb-Ramond field, and calculated the monopole’s quantized charge (an integer ) was decided.

This work shows how quantum simulators can be exploited in terms of studying abstract and complex physical structures, first introduced in the context of mathematical physics.