Short answer: A single erbium ion in silicon can be detected electrically by turning its optical excitation into a change of charge in a silicon transistor. A 2013 Nature paper reported this hybrid optical and electrical readout, and a later arXiv preprint (2212.00440) used radio-frequency reflectometry to detect a single erbium ion with sub-100-nanosecond time resolution and measure an excited-state lifetime of 0.49 microseconds. A third source, a 2018 Physical Review Letters paper on a telecom-band single-photon source, could be read only by title. These are single-ion laboratory experiments.

Why this matters

The 2013 Nature abstract says its approach "could drastically increase the range of defect centres that can be exploited" and represents a step toward interconnects between optical quantum computing and silicon technologies. That is the authors' framing.

2013: an optical trigger with an electrical readout

The Nature abstract notes that detection of single-defect electron spins had so far been accomplished for only two kinds of defect in crystalline solids: phosphorus dopants in silicon, with electrical readout through a single-electron transistor, and nitrogen-vacancy centers in diamond, with optical readout. A spin readout fidelity of about 90% had been demonstrated for both. The authors say thermal broadening limits the electrical scheme and poor photon collection limits the optical one, which makes higher fidelities hard.

They demonstrate a hybrid approach. Optical excitation changes the charge state, conditional on spin state, of an erbium defect centre in a silicon-based single-electron transistor, and the change is detected electrically. The high spectral resolution of the optical step overcomes the thermal limit, and the charge-sensing step avoids photon collection difficulties. The abstract does not report a spin readout fidelity for the erbium centre, so no figure is quoted here.

A later preprint: sub-100-nanosecond detection

The arXiv preprint 2212.00440 ("Photoionization detection of a single Er3+ ion with sub-100-ns time resolution") says efficient detection of single optical centers in solids is essential for quantum information, sensing and single-photon generation. The authors use radio-frequency reflectometry to electrically detect the photoionization induced by a single erbium ion in silicon. The high bandwidth and sensitivity give sub-100-nanosecond time resolution. With this, they measure the optically excited-state lifetime of a single erbium ion in a silicon nano-transistor for the first time, at 0.49 microseconds (uncertainty 0.04).

They say the approach could be used for fast readout of other single optical centers and is attractive for large-scale integrated optical quantum systems because multi-channel reflectometry was demonstrated with frequency multiplexing. The ar5iv text was read; this is a preprint, and its journal status is not shown.

The third source

A 2018 Physical Review Letters article is titled "Atomic Source of Single Photons in the Telecom Band". Its abstract could not be retrieved, so this post does not describe it.

Limits

Both experiments detect a single ion and report no quantum gate or entanglement. The 2013 paper does not report spin readout performance in the abstract, and the preprint's lifetime is a measurement from one device.

FAQ

How is the ion detected?

Optical excitation changes its charge state, which a silicon transistor senses electrically.

What lifetime was measured?

0.49 microseconds for the excited state, per the preprint.

Why is silicon attractive?

The 2013 authors say it connects to silicon technologies.

Is this a qubit demonstration?

Not in these abstracts. They describe detection.

What is RF reflectometry?

A fast, sensitive electrical measurement technique, used in the preprint.

All field notes