@antonfkockum.bsky.social
Quantum physicist (associate professor) at Chalmers University of Technology. Angel investor. Chess player and coach.
Now published in Physical Review Letters! @physrevlett.bsky.social
journals.aps.org/prl/abstract...
The many-body BICs we propose here should be accessible for state-of-the-art experiments using superconducting circuits.
(4/4)
Such spatially localised states in a continuum have previously mostly been studied for single photons/excitations.
(3/4)
We show that bound states in the continuum (BICs) can form with strongly correlated two-photon states, so-called doublons, in setups with atoms coupling at multiple points to a waveguide.
(2/4)
New preprint out today with my postdoc @guangzechen.bsky.social and Walter Rieck, at Chalmers University of Technology and the Wallenberg Centre for Quantum Technology:
”Doublon bound states in the continuum through giant atoms”
arxiv.org/abs/2511.18212
(1/4)
Our Python libraries for quantum state, process, and measurement tomography are freely available to use:
github.com/mstorresh/GD...
github.com/quantshah/gd...
github.com/agtomo/SGD-QMT
(5/5)
We now show how these data-processing methods also work well for extracting the POVM elements that characterise a measurement device.
(4/5)
We have previously developed and demonstrated such data-processing methods for quantum state and process tomography:
doi.org/10.1088/2058...
doi.org/10.1103/Phys...
(3/5)
In this work, we complete the tomography trio (state, process, and measurement tomography) with gradient-descent-based data-processing methods.
(2/5)
New preprint out this week with my postdoc @Akshay Gaikwad and Sebastian Torres:
”Quantum measurement tomography with mini-batch stochastic gradient descent”
arxiv.org/abs/2511.15682
(1/5)
Adding more physical coupling point to create an actual giant atom, we can make the scattering unidirectional and the conversion into a desired multi-photon state perfect.
(5/5)
The states with different numbers of photons naturally separate in space due to having different group velocities.
(4/5)
The scattering potential becomes nonlocal due to the spatial extension of the multi-photon states; we term this a pseudo-giant atom.
(3/5)
We show how correlated two- and three-photon states (doublons and triplons) can be generated by scattering an incoming single photon off excited two-level emitters in a nonlinear waveguide.
(2/5)
New preprint out today together with Jia-Qi Li and Xin Wang at Xi’an Jiaotong University: ”Generating spatially separated correlated multiphoton states in nonlinear waveguide quantum electrodynamics” arxiv.org/abs/2511.14281
(1/5)
Overall, we see better logical error suppression per amount of entanglement (ebits) than for other protocols, although it comes at the cost of an increased number of physical qubits to achieve the same code distance.
(7/7)
To avoid propagation of errors from the interface, we use an alternating sequence of syndrome-measurement circuits, which may be of independent interest.
(6/7)
Our protocol is based on an equivalence between Bell measurements and Bell pairs, which can be seen through ZX calculus.
(5/7)
In our work, we show how to perform lattice surgery (logical operations between encoded error-corrected qubits) across modules in a way that requires roughly half the amount of entanglement compared to previous protocols.
(4/7)
Thankfully, it has been shown that such an architecture can work even if the links between modules are more noisy than operations within modules. However, establishing entanglement between qubits on different modules is still a bottleneck.
(3/7)
Getting to well-functioning large-scale quantum computers will most likely require quantum error correction and a modular architecture, where several smaller processors are connected.
(2/7)
New preprint out today with Trond Haug, @timohillmann.bsky.social, and Raphaël Van Laer, at the Wallenberg Centre for Quantum Technology, Chalmers University:
”Lattice surgery with Bell measurements: Modular fault-tolerant quantum computation at low entanglement cost”
arxiv.org/abs/2510.13541
(1/7)
As an application, we show these three-qubit gates could rapidly generate high-fidelity highly entangled GHZ states among three and five giant atoms along a waveguide.
(6/6)
This draws inspiration from our previous work with these three-qubit gates in superconducting qubits(theory: link.aps.org/doi/10.1103/..., experiment: www.nature.com/articles/s41...), but works without tunable coupler elements and allows greater connectivity.
(5/6)
Here, we show that three giant atoms can be tuned to points where they don’t lose any energy into the waveguide, but exchange excitations through the waveguide to implement three-qubit CCZS and DIV gates.
(4/6)
Such setups can help quantum simulation of open quantum systems (iopscience.iop.org/article/10.1..., arxiv.org/abs/2503.04537).
(3/6)
We have previously shown how giant atoms, i.e., artificial atoms
coupled to a waveguide at multiple spatially separated points, can implement two-qubit iSWAP (www.nature.com/articles/s41...) and CZ gates (arxiv.org/abs/2503.04537) by making different transitions resonant.
(2/6)
New preprint out today with my Marie Curie postdoc Guangze Chen: ”Efficient three-qubit gates with giant atoms”, arxiv.org/abs/2510.04545
(1/6)
These results are promising for the continued progress towards large-scale quantum computers. The number of control lines in a quantum computer can be significantly reduced without introducing much overhead in execution time for quantum algorithms.
(5/5)
For single-qubit gates, we find that the serialization overhead generally scales only logarithmically in the number of qubits sharing a drive line. We are able to explain this finding using queueing theory.
(4/5)
