A coherent link between spatially separated nodes of a quantum network may be realized using itinerant photons as information carriers [1]. The necessary efficient absorption at the receiving node can be achieved by using a photon with a suitable temporal profile allowing time-reversal of the emission process [2].
Methods for generating shaped photons have recently been demonstrated in superconducting circuits [3]. In contrast with these schemes relying on fast flux biasing of the system, here we study a method which is fully microwavecontrolled [4]. We make use of the transmon’s second excited state and transfer its population into a resonator Fock state in a controlled way using a second-order transition driven by a classical coherent tone. The Fock state is subsequently emitted into the transmission line coupled to the resonator. We control the shape of this emitted photon by varying the rate of the second order transition in time. We also compensate the amplitude-dependent AC Stark shift induced by the strong drive with a suitable modulation of the drive phase. We demonstrate our scheme by preparing photon states with time-symmetric waveforms of controlled length. We also prepare photons with unusual multipeaked shapes and show that the phases of the peaks can be adjusted individually. Such photon states are potentially useful for encoding higher-dimensional quantum states [5] into a travelling quantum information carrier.

Figure 1.1: Symmetric photon waveforms of various lengths generated by the studied photon shaping process. The insets demonstrates stability of the photon phase.

Full article: https://journals.aps.org/prx/abstract/10.1103/PhysRevX.4.041010, also in arXiv:1308.4094