Description
The past decade has seen astounding progress in the field of digital quantum computation (QC). Traditionally, QC circuits consist of a set of coherent qubit operations, quantum gates, that are by definition unitary and therefore reversible. Parallel to the familiar use of quantum gates, a new paradigm of quantum information theory is emerging in which hybrid quantum-classic algorithms are proposed for tasks such as quantum simulation, machine learning, and optimization. For example, the simulation of open quantum systems will require an expansion of the current circuit toolbox, to include non-unitary operations. We present an experimental demonstration of a method of realizing controlled non-unitary operations, and use this tool to demonstrate two classic gates with ionic qubits: the OR and NOR operation. The state of one of the two qubits displays the output of the logical operations, and is dependent on the initial state of the two.
We apply the gates using two $^{40}$Ca$^{+}$ ions, trapped in a cryogenic segmented surface trap, as information carriers. The state is encoded in two of the ions' Zeeman sublevels, and is manipulated with optical light-fields. The gates employ engineered resonance through dressed state splitting, based on methods introduced in [1]: Resonant excitation of a two-qubit system transfers information about the two qubit state’s parity to a motional Fock state. Sympathetic cooling of a second co-trapped ion species, $^{80}$Sr$^{+}$, dissipatively removes the motional quanta, making the process non-unitary. We achieve an 87% population fidelity of the OR gate, and an 81% population fidelity of the NOR gate. The main sources of error in our experiments are limits in ground-state cooling of the ion crystal and a non-negligible increase in the motional mode occupation during the experimental sequences.
These experiments are a stepping stone towards an envisioned alternate scheme of quantum error correction (QEC). Conventional proposed QEC schemes rely on classical measurement and feedback to make decisions on whether to apply correction operations or not. Dissipation through engineered resonance prospectively has these decision making processes and correction operations built-in through the conditional state transfer mechanism.
[1] Reiter, F., Sørensen, A.S., Zoller, P. et al. Dissipative quantum error correction and application to quantum sensing with trapped ions. Nat Commun 8, 1822 (2017).
| Presenter name | Martin van Mourik |
|---|---|
| How will you attend ICAP-27? | I am planning on in-person attendance |
