Fig. 1 | Nature Communications

Fig. 1

From: Quantum wave mixing and visualisation of coherent and superposed photonic states in a waveguide

Fig. 1

Principles of the device operation. a A false coloured SEM image of the device: an electronic circuit (a superconducting four Josephson junction loop), behaving as an artificial atom, embedded into a transmission line, strongly interacts with propagating electromagnetic waves. b The four-wave mixing process results in the zero-one photon field creation at ω 3 = 2ω + − ω . In classical mixing, process \({a_ + }a_ - ^\dag {a_ + }b_3^ +\) comes in a pair with the symmetric one \({a_ - }a_ + ^\dag {a_ - }b_{ - 3}^ +\). In the mixing with non-classical states, the time-symmetry and, therefore, spectral symmetry are broken. c In QWM, the number of spectral peaks is determined by the number of photonic (Fock) states forming the superposed state in the atom. The state is created by the first pulse at ω and then mixed with the second pulse of ω +. Single-photon (N ph = 1) state \({\left| \beta \right\rangle _ - } = B\left( {\left| 0 \right\rangle + {\beta _ - }\left| 1 \right\rangle } \right)\)) can only create a peak at ω 3 = 2ω + − ω because only one photon at ω can be emitted from the atom. Two photon (N ph = 2) superposed state \({\left| \gamma \right\rangle _ - } = C\left( {\left| 0 \right\rangle + {\gamma _1}{{\left| 1 \right\rangle }_ - } + {\gamma _2}{{\left| 2 \right\rangle }_ - }} \right)\)) results in the creation of an additional peak at 3ω + − 2ω , because up to two photons can be emitted. Also two photons of ω can be absorbed, creating an additional left-hand-side peak at 2ω  − ω +

Back to article page