Characterization of the Si:Se+ Spin-Photon Interface

Silicon is the most-developed electronic and photonic technological platform and hosts some of the highest-performance spin and photonic qubits developed to date. A hybrid quantum technology harnessing an efficient spin-photon interface in silicon would unlock considerable potential by enabling ultralong-lived photonic memories, distributed quantum networks, microwave-to-optical photon converters, and spin-based quantum processors, all linked with integrated silicon photonics. However, the indirect band gap of silicon makes identification of efficient spin-photon interfaces nontrivial. Here we build upon the recent identification of chalcogen donors as a promising spin-photon interface in silicon. We determine that the spin-dependent optical degree of freedom has a transition dipole moment stronger than previously thought [here 1.96(8) D], and the spin T1 lifetime in low magnetic fields is longer than previously thought [here longer than 4.6(1.5) h]. We furthermore determine the optical excited-state lifetime [7.7(4) ns], and therefore the natural radiative efficiency [0.80(9)%], and by measuring the phonon sideband determine the zero-phonon emission fraction [16(1)%]. Taken together, these parameters indicate that an integrated quantum optoelectronic platform based on chalcogen-donor qubits in silicon is well within reach of current capabilities

A photonic platform for donor spin qubits in silicon

Donor spins in silicon are highly competitive qubits for upcoming quantum technologies, offering complementary metal-oxide semiconductor compatibility, coherence (T2) times of minutes to hours, and simultaneous initialization, manipulation, and readout fidelities near ~99.9%. This allows for many quantum error correction protocols, which will be essential for scale-up. However, a proven method of reliably coupling spatially separated donor qubits has yet to be identified. We present a scalable silicon-based platform using the unique optical properties of “deep” chalcogen donors. For the prototypical 77Se+ donor, we measure lower bounds on the transition dipole moment and excited-state lifetime, enabling access to the strong coupling limit of cavity quantum electrodynamics using known silicon photonic resonator technology and integrated silicon photonics. We also report relatively strong photon emission from this same transition. These results unlock clear pathways for silicon-based quantum computing, spin-to-photon conversion, photonic memories, integrated single-photon sources, and all-optical switches

Towards optical readout of Si:Se+

The demonstration of a qubit system in silicon, with efficient optical control and readout of robust electronic and nuclear spin states, would change the current dominant industrial trends in quantum devices. Singly ionized deep double donors in silicon (Si:Se+) have shown promise as examples of such industry-changing qubit candidates. The (Si:Se+) system possesses a long-lived spin qubit with photonic access through a spin-selective optical transition. Under the assumption that this optical transition is radiatively efficient, it has been proposed that this optical transition be exploited for direct emission-based spin-state readout, or alternatively used as a much-sought-after silicon-integrated single-photon source. In the first part of this thesis, we present the measurement of the T1 lifetime of the optically excited state which in turn allowed us to determine a natural radiative efficiency of 0.80(1)%. Fortunately, this spin-photon interface can be coupled to photonic cavity modes for indirect spin-state read-out or to improve the emission rate through the Purcell effect. In the second part of this thesis, we present the hardware and software details of an adaptable automated photonics testing system that can be used to characterize integrated photonic devices