Quantum phononics
Strain tuning of solid-state defects
Solid state defects are one of the leading platforms for both on-demand single photon emitters as well as optically accessible quantum memories [1- 2]. While there have been numerous demonstrations of individual spin control and deterministic single photon sources from a single device, scaling these devices remains challenging. Local environmental differences lead to perturbed electronic structures, causing defects to emit at slightly different frequencies.
Strain tuning, the process of modifying the electronic structure of a point defect through the application of static strain, is the most natural approach to tune these centers [3]. This approach provides a clear pathway to creating
large arrays of indistinguishable emitters.
References:
[1] P.-J. Stas, Y. Q. Huan, B. Machielse, E. N. Knall, A. Suleymanzade, B. Pingault, M. Sutula, S. W. Ding, C. M. Knaut, D. R. Assumpcao, Y.-C. Wei, M. K. Bhaskar, R. Riedinger, D. D. Sukachev, H. Park, M. Lonˇcar, D. S. Levonian, and M. D. Lukin, “Robust multi-qubit quantum network node with integrated error detection,” Science, vol. 378, no. 6619, pp. 557–560, 2022.
[2] L. Komza, P. Samutpraphoot, M. Odeh, Y.-L. Tang, M. Mathew, J. Chang, H. Song, M.-K. Kim, Y. Xiong, G. Hautier, and A. Sipahigil, “Indistinguishable photons from an artificial atom in silicon photonics,” 2022.
[3] S. Meesala, Y.-I. Sohn, B. Pingault, L. Shao, H. A. Atikian, J. Holzgrafe, M. G ̈undo ̆gan, C. Stavrakas, A. Sipahigil, C. Chia, R. Evans, M. J. Burek, M. Zhang, L. Wu, J. L. Pacheco, J. Abraham, E. Bielejec, M. D. Lukin, M. Atat ̈ure, and M. Lonˇcar, “Strain engineering of the silicon-vacancy center in diamond,” Phys. Rev. B, vol. 97, p. 205444, May 2018.
High-fidelity trapped-ion qubit operations with scalable photonic modulators
Ion-trapping technology has matured to the point that traps are being microfabricated on chips, like the Phoenix trap at Sandia National Laboratories.
Calcium ions contain a 2-level system with a transition driven by 729 nm light which can function as a qubit. These trapped-ion quantum computers require precise optical modulation in order to drive the transitions of the ions and thus perform gate operations on the qubits. The focus of our group is on the optical control and its scalability. Since every qubit requires a unique optical signal, producing beams off-chip and edge-coupling them with fibers quickly becomes unsuitable because the number of ions can grow as the area of the chip while the edge-coupling I/O grows with its perimeter. The solution is to input a single optical signal onto the chip and then split the light with waveguide beamsplitters into the desired number of separate channels which are then individually modulated by an electrical signal.
Our group has produced a device employing the aforementioned approach using piezoelectrically actuated Mach-Zender modulators (MZMs).
The MZMs consist of a waveguide layer acting as two Mach-Zender interferometers, which sit above a piezoelectric substrate sandwiched between electrodes. When voltage is applied to the electrodes, the piezo-material is strained which in turn strains the waveguide and produces a change in phase along one of the waveguide-arms relative to other. In this way the signal entering the MZM can be amplitude modulated as a function of the voltage applied to the electrodes. Computational gates (rotations about the X and Y axes of the Bloch sphere) and the identity gate implemented with one of these MZM-based devices yielded gate-fidelities exceeding 99.7%. These results show that the modulators perform on-par with the state of the art and in principle can scale with the number of qubits needed for true, large-scale trapped-ion quantum computers.
References:
[1] High-fidelity trapped-ion qubit operations with scalable photonic modulators, C. W. Hogle, D. Dominguez, M. Dong, A. Leenheer, H. J. McGuinness, B. P. Ruzic, M. Eichenfield, and D. Stick1, arXiv:2210.14368 2022.