RAISIN Webinar on 3 November

Pioneering platform for integrated quantum memories donor qubits:
synthesis and isolation of single donors

On Thursday 3rd of November at 3pm (GMT), you can join a RAISIN webinar with Margherita Mazzera from Heriot-Watt University at
https://surrey-ac.zoom.us/j/95487006700 – or access it through the RAISIN website.

Pioneering platform for integrated quantum memories donor qubits: synthesis and isolation of single donors

Margherita Mazzera, Heriot-Watt University

The coherent interaction between photons and atoms lays the bases of quantum information science, whose purpose is to open new possibilities for the transmission and the processing of information. It is crucial, e.g., for the realisation of quantum networks. Solid-state systems have emerged as promising platforms; more specifically rare earth ion doped crystals are one of the most interesting candidates. The implementation of quantum memory protocols in waveguide has the potential of opening further avenues towards scalable quantum information protocols using complex quantum photonic circuits on chip.

Our approach is based on fs-laser written waveguides (LWW) fabricated in an insulating crystal which has proven outstanding performances as interface between single photons and single atomic or spin excitations, i.e. Pr:YSO [1]. The new writing regime adopted gave, with respect to previous demonstration in the same material, sensibly smaller guiding modes, with diameter compatible with the core of telecom fibres, but lower insertion and bending losses. Given the simplicity and versatility of the fabrication, its unique 3D capability and the outstanding storage performance, the demonstration represented a change of paradigm in the quest for integrated quantum memories. We demonstrated that this integrated platform for the storage of quantum states of light [2], also enabled the storage of more than 100 spectro-temporal modes [3] and the storage of photonic entanglement in a fibre-integrated device [4]. However, much has to be demonstrated yet with this platform, e.g., the on-demand storage of single photons. One major problem is that the integrated storage devices might prove more prone to photonic noise due to light confinement, as the single photon inputs travel in the same spatial mode as the high intensity pulses used for on-demand storage and retrieval.

We propose here two alternative routes to overcome this problem and perform on-demand storage in waveguides. One is to implement a gradient echo memory [5]. This scheme relies on the manipulation of the spectral absorption profile of an atomic ensemble by means of static electric fields to efficiently absorb and coherently reemit a light pulse. The significant advantage of the compact design is that metallic contacts can be deposited very close to the waveguide (about 100 μm), thus enabling the electrical control of the atomic resonances with limited voltage and with negligible cross-talk between adjacent waveguides. The other strategy is to complement the most widely used storage protocol for multimode quantum storage, the atomic frequency comb [6], with the off-resonant cascaded absorption protocol [7], originally proposed for warm vapours featuring a ladder-type energy level scheme. We expect this combined protocol to enable the storage of broadband photons, thanks to the enhancement of the light-matter inteaction in waveguides, while not being affected by photonic noise, because of the large separation in frequency between the single photon input and the high power pulses for the on-demand storage.

Finally, I will also discuss how, being able to deterministically position the rare earth ions at specific sites, at distances closely related to the operating wavelengths, would allow us exploiting super- and sub-radiance mechanisms of the ordered ensembles to enhance or suppress the photon emission and the storage efficiency in a controllable fashion. Moreover, the potential of exploiting each single rare earth ion as an independently addressable single photon source would open new avenues for the scalable spatial multiplexing of local quantum processors.

[1] A. Seri et al, Phys. Rev. X 7, 021028 (2017) ; K. Kutluer et al, Phys. Rev. Lett. 118, 210502 (2017).

[2] A. Seri et al, Optica 5(8) (2018) 934
[3] A. Seri et al, Phys. Rev. Lett. 123 (2019) 080502
[4] J. V. Rakonjac et al, Science Advances 8 (2022) eabn3919

[5] M. Nilsson et al, Opt.Com. 247 (2005) 393
[6] M. Afzelius et al, Physical Review A 79 (2009) 052329
[7] K.T. Kaczmarek et al, Physical Review A 97 (2018) 042316