Radios are shrinking. Normal radio receivers use an antenna tuned to a particular range of frequencies, but now researchers have developed an atomic receiver in a tiny glass box that is excellent for spying.
David Anderson at Rydberg Technologies in Michigan and his colleagues built their radio receiver to be more secure and smaller than traditional radios. It starts with a centimetre-sized glass box full caesium vapour. The caesium atoms are prepared so that some of the electrons have more energy than normal, which makes them highly sensitive to certain frequencies of electromagnetic waves.
Radio transmissions work by modulating an electromagnetic wave鈥檚 amplitude or frequency 鈥� for AM and FM radio, respectively 鈥� to encode the sound that you want to transmit. The waves are generally received by an antenna, which converts them into electricity. Then speaker circuits turn those electrical signals into sounds.
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In this radio receiver, the caesium atoms act as the antenna. When an electromagnetic wave hits the atoms, it temporarily bumps some of their electrons up to a higher energy level, changing the quantum state of the atom.
To turn that into sound, the team shone a laser through the box. Atoms in different states absorb laser light differently, so measuring the light that passes through reveals the quantum states of the atoms. This in turn can be translated back into the original signal.
The main benefit to this method 鈥� aside from its compact size 鈥� is that unlike traditional radio receivers, it works in multiple frequency bands, well beyond what a car radio can pick up, Anderson says.
While the laser readout makes it impossible to, say, put this receiver in a tooth to receive covert messages, it could be used for spying, Anderson says. 鈥淚f you think about a scanning spy radio, trying to pick up someone talking, you could scan all kinds of secure channels that are in the area,鈥� he says. 鈥淚nstead of requiring multiple types of antenna at a receiving station, you could use one vapour receiver to do all of it.鈥�
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