The preferred format for the answer would be similar to:
"Group ABC's method DEF has demonstrated better QV than using MF; as proven independently in paper G on page x, paper H on page y, and paper I on page z".
These particles could be the elementary brick of topological quantum computers, with very strong protection against errors. Our work is an initial step in this direction.
Example of an insufficient (but interesting) answer:
In their paper "Robust quantum metrological schemes based on protection of quantum Fisher information", Xiao-Ming Lu, Sixia Yu, and C.H. Oh construct a family of $2t+1$ qubits metrological schemes being immune to $t$-qubit errors after the signal sensing. In comparison at least five qubits are required for correcting arbitrary 1-qubit errors in standard quantum error correction.
[Note: This theory of robust metrological schemes preserves the quantum Fisher information instead of the quantum states themselves against noise. That results in a good effective volume if they can construct a device utilizing their techniques and show that it scales.
While that might seem like one promising answer it's a single link (without multiple concurring sources) and there's no device built to show scalability. A low qubit device that's error free and unscalable or a device with many error-prone qubits has a low volume (and thus is "Not An Answer").]
Paper explaining Quantum Volume.
After doing some research it looks like Graphene sandwiched between superconductors to produce Majorana fermions is the leading edge - is there something better? ["better" means currently possible, not theoretically possible or ridiculously expensive]. The graphic illustrates that over a hundred qubits with less 0.0001 error rate is wonderful, lesser answers are acceptable.