Ross DuncanToday, a bunch of my colleagues posted a preprint demonstrating, for the first time, a 3-qubit QFT, under a CSS code with noisy T states. Tomorrow, one of those colleagues, Natalie Brown, will be giving an invited talk at #qctip!
Benchmarking logical three-qubit quantum Fourier transform encoded in the Steane code on a trapped-ion quantum computer
We implement logically encoded three-qubit circuits for the quantum Fourier transform (QFT), using the [[7,1,3]] Steane code, and benchmark the circuits on the Quantinuum H2-1 trapped-ion quantum computer. The circuits require multiple logical two-qubit gates, which are implemented transversally, as well as logical non-Clifford single-qubit rotations, which are performed by non-fault-tolerant state preparation followed by a teleportation gadget. First, we benchmark individual logical components using randomized benchmarking for the logical two-qubit gate, and a Ramsey-type experiment for the logical $T$ gate. We then implement the full QFT circuit, using two different methods for performing a logical control-$T$, and benchmark the circuits by applying it to each basis state in a set of bases that is sufficient to lower bound the process fidelity. We compare the logical QFT benchmark results to predictions based on the logical component benchmarks.