Research

Logical operations on single-ion logical qubits

We developed and demonstrated a novel entangling gate for multi-level qudits using trapped 40Ca+ ions, enabling high-fidelity logical operations on single-ion logical qubits encoded in the six-level D5/2 manifold. This operation can also be used to create a maximally-entangled two-qudit state in a single application of the interaction.

Using spin-cat codewords, we implemented a universal set of logical gates, including a controlled-phase gate between two logical qubits in separate ions.

More info coming soon!

Single-ion error correction

Schematic of trapped-ion qudit error correction showing spin-cat encoding, circuit diagram with encoding, error, decoding, and correction, plus D5/2 energy levels coupled by RF and blue sideband transitions to S1/2 states.

I led an experiment demonstrating quantum error correction within a single 40Ca+ ion by encoding a logical qubit in the six-level spin-5/2 manifold using spin-cat codewords. A measurement-free (autonomous) recovery uses the ion’s motional mode as a resettable ancilla, suppressing dephasing: logical error is reduced by up to 2.2× and the useful coherence time extends by up to 1.5× relative to an unencoded qubit.

This work represents the first demonstration of qudit-based quantum error correction in a single particle. Using high-fidelity operations in the D5/2 manifold together with spin-motion coupling, we implement encoding, decoding, and autonomous correction without requiring mid-circuit measurements. The approach provides hardware-efficient protection against the dominant dephasing mechanism and opens the door to more tailored error correction codes to be used in a variety of applications.

Real-time noise tracking and feedforward with monitor ions

Energy level diagrams of two trapped ions. (a) Data ion: qubit encoded in S1/2 states with 13 MHz RF coupling and connection to D5/2 manifold. (b) Monitor ion: qubit encoded in D5/2 states with 729 nm optical transitions and coupling for magnetic field sensing.

We demonstrate a trapped-ion protocol in which a dedicated "monitor" qubit tracks magnetic-field drifts in real time without interrupting data-qubit operations. Using two 40Ca+ ions and the optical–metastable–ground architecture, we encode the data qubit in the ground-state manifold and the monitor qubit in a metastable-state manifold to achieve spectral separation. The monitor qubit senses magnetic fluctuations during data-qubit experiments, enabling feedforward corrections. Under applied 1/f2 magnetic noise, the protocol maintains coherence, extends usable probe times by up to √2 compared with interleaved calibration, and doubles experimental throughput. These results establish monitor qubits as a scalable tool for real-time recalibration in quantum processors.

Quantum channel discrimination using quantum signal processing

Two 3D bar charts comparing quantum channel discrimination results. Left: Accuracy plot showing near-unity population for correct measured states at signal angles 0, 2π/3, and 4π/3. Right: Error plot showing small residual population inaccuracies, all below about 0.012.

We demonstrate accurate, single-shot discrimination among three quantum channels using a single trapped 40Ca+ ion. Leveraging the six-level D5/2 metastable manifold and quantum signal processing (QSP), we implement trapped-ion analogues of phase-shift-keying (PSK) and amplitude-shift-keying (ASK) protocols and achieve >99% discrimination accuracy—limited only by characterized experimental imperfections. The protocol scales to larger channel sets with finite queries and highlights the utility of metastable qudit states for advanced quantum communication and sensing tasks.