The unrelenting advancement of modern technology has inadvertently allowed the production of counterfeit components to become increasingly cheaper and easier, undermining the trust of everyday interactions and communications.

An emerging solution to this problem is the use of physically unclonable functions1 (PUFs) - physical devices with random characteristics locked into their structure at the point of fabrication. The application of a stimulus to these constructions results in a hard-to-predict response due to the interaction with the complex microstructure of the device. This response is then used as a 'fingerprint' that can be used for a given application. Among others, these include low-cost device identification and authentication, secure key generation and the binding of software to hardware platforms. However, traditional PUFs have various setbacks: they suffer from not being truly unclonable, are susceptible to sophisticated attacks and bear a risk of emulation and simulation.

Here we show that quantum physics lends itself to the provision of unique identities in the form of fluctuations in measurements of resonant tunnelling diodes (RTDs) containing various nanostructures. An example of which is a quantum dot, shown in Fig. 1. This provides an uncomplicated measure of identity, without conventional resource limitations or vulnerabilities. The quantum tunnelling spectrum also shown in Fig. 1 is sensitive to the atomic structure within the RTD, with each device providing extreme uniqueness that is presently impossible to clone or simulate. This new class of authentication device, coined the quantum unclonable function (QUF)2, operate with the fewest resources in simple electronic structures operating above 300 K.