Quantum Science and Technology

Journal: Quantum Science and Technology

Abbreviation

Quantum Sci. Technol.

Publisher

IOP Publishing

ISSN

2058-9565

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Publications 1 - 10 of 25

Variational quantum thermalizers based on weakly-symmetric nonunitary multi-qubit operations
Zapusek, Elias; Kirova, Kristina; Hahn, Walter; et al. (2026)
Quantum Science and Technology
We propose incorporating multi-qubit nonunitary operations in variational quantum thermalizers (VQTs). VQTs are hybrid quantum-classical algorithms that generate the thermal (Gibbs) state of a given Hamiltonian, with applications in quantum algorithms and simulations. However, current algorithms struggle at intermediate temperatures, where the target state is nonpure but exhibits entanglement. We devise multi-qubit nonunitary operations that harness weak symmetries and thereby improve the performance of the algorithm. Utilizing dissipation engineering, we create these nonunitary multi-qubit operations without the need for measurements or additional qubits. To train the ansatz, we develop and benchmark novel methods for entropy estimation of quantum states, expanding the toolbox for quantum state characterization. We demonstrate that our approach can prepare thermal states of paradigmatic spin models at all temperatures. Our work thus creates new opportunities for simulating open quantum many-body systems.
Applying electric and magnetic field bias in a 3D superconducting waveguide cavity with high quality factor
Stammeier, Mathias; Garcia, Sébastien; Wallraff, Andreas (2018)
Quantum Science and Technology
On-chip tunable quantum interference in a lithium niobate-on-insulator photonic integrated circuit
Maeder, Andreas; Finco, Giovanni; Kaufmann, Fabian; et al. (2024)
Quantum Science and Technology
Programmable interferometric circuits are at the heart of integrated quantum photonic processors. While the lithium niobate-on-insulator platform has the potential to advance integrated quantum photonics due to its strong nonlinearity and tight mode confinement, the demonstration of reconfigurable two-photon interference has not yet been achieved. Here, we design, fabricate and characterize the building block of such interferometric networks in the form of a 2x2 Mach-Zehnder Interferometer. We use a thermo-optic phase shifter to achieve stable performance with a power consumption of Pπ = 44.4 mW and sub-microsecond switching times. We demonstrate the effectiveness of our device for quantum applications by measuring single-photon routing with up to 34 dB extinction ratio. We show Hong-Ou-Mandel interference with fully tunable visibilities reaching a maximum value of 97.4 ± 1.0 %. As part of large scale quantum photonic circuits, this building block will facilitate reconfigurable and tunable photonic processing units integrated alongside non-classical light sources.
Research campaign: Macroscopic quantum resonators (MAQRO)
Kaltenbaek, Rainer; Arndt, Markus; Aspelmeyer, Markus; et al. (2023)
Quantum Science and Technology
The objective of the proposed macroscopic quantum resonators (MAQRO) mission is to harness space for achieving long free-fall times, extreme vacuum, nano-gravity, and cryogenic temperatures to test the foundations of physics in macroscopic quantum experiments at the interface with gravity. Developing the necessary technologies, achieving the required sensitivities and providing the necessary isolation of macroscopic quantum systems from their environment will lay the path for developing novel quantum sensors. Earlier studies showed that the proposal is feasible but that several critical challenges remain, and key technologies need to be developed. Recent scientific and technological developments since the original proposal of MAQRO promise the potential for achieving additional science objectives. The proposed research campaign aims to advance the state of the art and to perform the first macroscopic quantum experiments in space. Experiments on the ground, in micro-gravity, and in space will drive the proposed research campaign during the current decade to enable the implementation of MAQRO within the subsequent decade.
Quantum teleportation of cat states with binary-outcome measurements
Feng, Jingyan; Zhang, Mohan; Fadel, Matteo; et al. (2025)
Quantum Science and Technology
We propose a teleportation protocol involving beam splitting operations and binary-outcome measurements, such as parity measurements. These operations have a straightforward implementation using the dispersive regime of the Jaynes-Cummings Hamiltonian, making our protocol suitable for a broad class of platforms, including trapped ions, circuit quantum electrodynamics and acoustodynamics systems. In these platforms homodyne measurements of the bosonic modes are less natural than dispersive measurements, making standard continuous variable teleportation unsuitable. In our protocol, Alice is in possession of two bosonic modes and Bob a single mode. An entangled mode pair between Alice and Bob is created by performing a beam splitter operation on a cat state. An unknown qubit state encoded by cat states is then teleported from Alice to Bob after a beamsplitting operation, measurement sequence, and a conditional correction. In the case of multiple measurements, near-perfect fidelity can be obtained. We discuss the optimal parameters in order to maximize the fidelity under a variety of scenarios.
Building blocks of a flip-chip integrated superconducting quantum processor
Kosen, Sandoko; Li, Hang-Xi; Rommel, Marcus; et al. (2022)
Quantum Science and Technology
We have integrated single and coupled superconducting transmon qubits into flip-chip modules. Each module consists of two chips – one quantum chip and one control chip – that are bump-bonded together. We demonstrate time-averaged coherence times exceeding 90 μs, single-qubit gate fidelities exceeding 99.9%, and two-qubit gate fidelities above 98.6%. We also present device design methods and discuss the sensitivity of device parameters to variation in interchip spacing. Notably, the additional flip-chip fabrication steps do not degrade the qubit performance compared to our baseline state-of-the-art in single-chip, planar circuits. This integration technique can be extended to the realisation of quantum processors accommodating hundreds of qubits in one module as it offers adequate input/output wiring access to all qubits and couplers.
Optimal control of spin qudits subject to decoherence using amplitude-and-frequency-constrained pulses
Hernández-Antón, Alonso; Luis, Fernando; Castro, Alberto (2025)
Quantum Science and Technology
Quantum optimal control theory (QOCT) can be used to design the shape of electromagnetic pulses that implement operations on quantum devices. By using non-trivially shaped waveforms, gates can be made significantly faster than those built by concatenating monochromatic pulses. Recently, we applied this idea to the control of molecular spin qudits modeled with Schr & ouml;dinger's equation and showed it can speed up operations, helping mitigate the effects of decoherence (Castro et al 2022 Phys. Rev. Appl. 17 064028). However, short gate times require large optimal pulse amplitudes, which may not be experimentally accessible. Introducing bounds to the amplitudes then unavoidably leads to longer operation times, for which decoherence can no longer be neglected. Here, we study how to improve this procedure by applying QOCT on top of Lindblad's equation, to design control pulses accounting for decoherence already in the optimization process. We define the control signal in terms of generic parameters, which permits the introduction of bounds and constraints. This is convenient, as amplitude and frequency limitations are inherent to waveform generators. The pulses that we obtain consistently enhance operation fidelities compared to those achieved with the optimization based on Schr & ouml;dinger's equation, demonstrating the flexibility and robustness of our method. The improvement is larger the shorter the spin coherence time T2.
Quantum correlations in molecules: from quantum resourcing to chemical bonding
Ding, Lexin; Knecht, Stefan; Zimborás, Zoltán; et al. (2023)
Quantum Science and Technology
The second quantum revolution is all about exploiting the quantum nature of atoms and molecules to execute quantum information processing tasks. To boost this growing endeavor and by anticipating the key role of quantum chemistry therein, our work establishes a framework for systematically exploring, quantifying and dissecting correlation effects in molecules. By utilizing the geometric picture of quantum states we compare-on a unified basis and in an operationally meaningful way-total, quantum and classical correlation and entanglement in molecular ground states. To unlock and maximize the quantum informational resourcefulness of molecules an orbital optimization scheme is developed, leading to a paradigm-shifting insight: a single covalent bond equates to the entanglement 2ln(2)
Roadmap on quantum thermodynamics
Campbell, Steve; D'amico, Irene; Ciampini, Mario A.; et al. (2026)
Quantum Science and Technology
The last two decades have seen quantum thermodynamics become a well established field of research in its own right. In that time, it has demonstrated a remarkably broad applicability, ranging from providing foundational advances in the understanding of how thermodynamic principles apply at the nano-scale and in the presence of quantum coherence, to providing a guiding framework for the development of efficient quantum devices. Exquisite levels of control have allowed state-of-the-art experimental platforms to explore energetics and thermodynamics at the smallest scales which has in turn helped to drive theoretical advances. This Roadmap provides an overview of the recent developments across many of the field's sub-disciplines, assessing the key challenges and future prospects, providing a guide for its near term progress.
Physical coherent cancellation of optical addressing crosstalk in a trapped-ion experiment
Flannery, Jeremy; Matt, Roland; Huber, Luca Immanuel; et al. (2025)
Quantum Science and Technology
We present an experimental investigation of coherent crosstalk cancellation methods for light delivered to a linear ion chain cryogenic quantum register. The ions are individually addressed using focused laser beams oriented perpendicular to the crystal axis, which are created by imaging each output of a multi-core photonic-crystal fibre waveguide array onto a single ion. The measured nearest-neighbor native crosstalk intensity of this device for ions spaced by 5 μm is found to be ~10⁻². We show that we can suppress this intensity crosstalk from waveguide channel coupling and optical diffraction effects by a factor >10³ using cancellation light supplied to neighboring channels which destructively interferes with the crosstalk. We measure a rotation error per gate on the order of εₓ similar to 10⁻⁵ on spectator qubits, demonstrating a suppression of crosstalk error by a factor of >10². We compare the performance to composite pulse methods for crosstalk cancellation, and describe the appropriate calibration methods and procedures to mitigate phase drifts between these different optical paths, including accounting for problems arising due to pulsing of optical modulators.

Publications 1 - 10 of 25

Journal: Quantum Science and Technology

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