Anton Frisk Kockum
@antonfkockum.bsky.social
Quantum physicist (associate professor) at Chalmers University of Technology. Angel investor. Chess player and coach.
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.
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October 16, 2025 at 6:34 PM
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.
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To avoid propagation of errors from the interface, we use an alternating sequence of syndrome-measurement circuits, which may be of independent interest.
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October 16, 2025 at 6:33 PM
To avoid propagation of errors from the interface, we use an alternating sequence of syndrome-measurement circuits, which may be of independent interest.
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Our protocol is based on an equivalence between Bell measurements and Bell pairs, which can be seen through ZX calculus.
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October 16, 2025 at 6:33 PM
Our protocol is based on an equivalence between Bell measurements and Bell pairs, which can be seen through ZX calculus.
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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.
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October 16, 2025 at 6:32 PM
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.
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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.
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October 16, 2025 at 6:32 PM
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.
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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.
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October 16, 2025 at 6:32 PM
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.
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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.
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October 7, 2025 at 11:56 AM
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.
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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.
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Fast Multiqubit Gates through Simultaneous Two-Qubit Gates
A recipe to create multi-qubit gates that uses existing quantum hardware-- without any additional components, complicated pulse shapes, or changes in design--is proposed, promising a reduction in circ...
link.aps.org
October 7, 2025 at 11:55 AM
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.
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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.
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October 7, 2025 at 11:55 AM
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.
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Such setups can help quantum simulation of open quantum systems (iopscience.iop.org/article/10.1..., arxiv.org/abs/2503.04537).
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iopscience.iop.org
October 7, 2025 at 11:55 AM
Such setups can help quantum simulation of open quantum systems (iopscience.iop.org/article/10.1..., arxiv.org/abs/2503.04537).
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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.
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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.
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Waveguide quantum electrodynamics with superconducting artificial giant atoms - Nature
Superconducting giant atoms are realized in a waveguide by coupling small atoms to the waveguide at multiple discrete locations, producing tunable atom–waveguide coupling and enabling decoherence-free interactions.
www.nature.com
October 7, 2025 at 11:54 AM
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.
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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.
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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.
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August 29, 2025 at 11:32 AM
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.
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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.
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August 29, 2025 at 11:32 AM
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.
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We quantify this trade-off and find it to be surprisingly benign. We show that couplers for two-qubit gates can be grouped on common drive lines without any overhead up to a limit set by the connectivity of the qubits.
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August 29, 2025 at 11:32 AM
We quantify this trade-off and find it to be surprisingly benign. We show that couplers for two-qubit gates can be grouped on common drive lines without any overhead up to a limit set by the connectivity of the qubits.
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We want to limit the number of control lines going into the fridge hosting qubits, to reduce cooling requirements and electronics. But this risks quantum algorithms taking longer to execute and becoming affected by noise, since fewer qubits can be controlled in parallel.
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August 29, 2025 at 11:31 AM
We want to limit the number of control lines going into the fridge hosting qubits, to reduce cooling requirements and electronics. But this risks quantum algorithms taking longer to execute and becoming affected by noise, since fewer qubits can be controlled in parallel.
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In this way, we improve on traditional Purcell filters without actually needing to introduce additional components on the chip, saving valuable space when scaling up superconducting quantum computers.
July 15, 2025 at 10:14 AM
In this way, we improve on traditional Purcell filters without actually needing to introduce additional components on the chip, saving valuable space when scaling up superconducting quantum computers.
By introducing asymmetries in the qubit geometry, we activate couplings between several higher-frequency modes, which in turn creates destructive interference that cancel Purcell decay through the main readout-resonator mode.
arxiv.org/abs/2507.09715
arxiv.org/abs/2507.09715
Intrinsic Multi-Mode Interference for Passive Suppression of Purcell Decay in Superconducting Circuits
Decoherence due to radiative decay remains an important consideration in scaling superconducting quantum processors. We introduce a passive, interference-based methodology for suppressing radiative de...
arxiv.org
July 15, 2025 at 10:13 AM
By introducing asymmetries in the qubit geometry, we activate couplings between several higher-frequency modes, which in turn creates destructive interference that cancel Purcell decay through the main readout-resonator mode.
arxiv.org/abs/2507.09715
arxiv.org/abs/2507.09715
Now published in Applied Physics Letters! pubs.aip.org/aip/apl/arti...
Tunable coherent microwave beam splitter and combiner at the single-photon level
A beam splitter is a key component used to direct and combine light paths in various optical and microwave systems. It plays a crucial role in devices like inte
pubs.aip.org
July 8, 2025 at 4:31 PM
Now published in Applied Physics Letters! pubs.aip.org/aip/apl/arti...
Check it out at arxiv.org/abs/2505.23860. My own contribution was mainly on how AI can help quantum computers. (2/2)
June 2, 2025 at 1:18 PM
Check it out at arxiv.org/abs/2505.23860. My own contribution was mainly on how AI can help quantum computers. (2/2)