arXiv subjects

Axel M. Eriksson

Publications and source records attributed to Axel M. Eriksson.

8 recordsLinked to original sources

arXiv2026

Error Mitigation in Bosonic Systems via Virtual Distillation

Virtual distillation is a promising error-mitigation technique that exploits multiple copies of a noisy quantum state to estimate observables as if measured on a purified state. Although originally introduced in the context of bosonic many-body systems under the name of virtual cooling, its development and applications have largely focused on qubit-based quantum computation. Here, we establish a framework for virtual distillation in bosonic quantum information processing and continuous-variable quantum computing. Building on a diagonalization of cyclic shift operators implemented with passive linear-optical interferometers, we derive experimentally accessible protocols for estimating virtually distilled expectation values of observables relevant to bosonic architectures. In particular, we show how to recover noise-mitigated expectation values of number operators, phase-shift operators, and arbitrary quadratures from multi-copy measurements. For number operators, we further demonstrate the estimation of virtually distilled correlators of arbitrary order through the characteristic function of the photon-number distribution. We apply the framework to states affected by photon loss and dephasing, two of the dominant noise mechanisms in bosonic quantum computation, and quantify the resulting suppression of noise contributions. Our results extend virtual distillation beyond its original setting and provide a practical route toward error-mitigated measurements in bosonic quantum processors using experimentally available linear-optical resources.

quant-ph↗

arXiv2025

Effective Hamiltonian for an off-resonantly driven qubit-cavity system

Accurate modeling of driven light-matter interactions is essential for quantum technologies, where natural and synthetic atoms are used to store and process quantum information, mediate interactions between bosonic modes, and enable nonlinear operations. In systems subject to multi-tone drives, however, the theoretical description becomes challenging and existing models cannot quantitatively reproduce the experimental data. Here, we derive an effective Hamiltonian that retains slowly rotating terms, providing a general framework for accurately describing driven dynamics across platforms. As a concrete application, we validate the theory in circuit QED, where it quantitatively reproduces experimentally measured ac Stark shifts and captures key interactions such as two-mode squeezing and beam-splitting. Our results establish a broadly applicable tool to engineer driven interactions in quantum information processing platforms.

quant-ph↗

arXiv2025

Automated, physics-guided, multi-parameter design optimization for superconducting quantum devices

The design of nonlinear superconducting quantum circuits often relies on time-consuming iterative electromagnetic simulations requiring manual intervention. These interventions entail, for example, adjusting design variables such as resonator lengths or Josephson junction energies to meet target parameters such as mode frequencies, decay rates, and coupling strengths. Here, we present a method to efficiently automate the optimization of superconducting circuits, which significantly reduces the need for manual intervention. The method's efficiency arises from user-defined, physics-informed, nonlinear models that guide parameter updates toward the desired targets. Additionally, we provide a full implementation of our optimization method as an open-source Python package, QDesignOptimizer. The package automates the design workflow by combining high-accuracy electromagnetic simulations in Ansys HFSS and Energy Participation Ratio (pyEPR) analysis integrated with the design tool Qiskit-Metal. Our implementation supports modular and flexible subsystem-level analysis and is easily extensible to optimize for additional parameters. The method is not specific to superconducting circuits; as such, it can be applied to a range of nonlinear optimization problems across science and technology.

quant-ph↗

arXiv2024

Direct detection of quasiparticle tunneling with a charge-sensitive superconducting sensor coupled to a waveguide

Detecting quasiparticle tunneling events in superconducting circuits provides information about the population and dynamics of non-equilibrium quasiparticles. Such events can be detected by monitoring changes in the frequency of an offset-charge-sensitive superconducting qubit. This monitoring has so far been performed by Ramsey interferometry assisted by a readout resonator. Here, we demonstrate a quasiparticle detector based on a superconducting qubit directly coupled to a waveguide. We directly measure quasiparticle number parity on the qubit island by probing the coherent scattering of a microwave tone, offering simplicity of operation, fast detection speed, and a large signal-to-noise ratio. We observe tunneling rates between 0.8 and $7~\rm{s}^{-1}$, depending on the average occupation of the detector qubit, and achieve a temporal resolution below $10~μ\rm{s}$ without a quantum-limited amplifier. Our simple and efficient detector lowers the barrier to perform studies of quasiparticle population and dynamics, facilitating progress in fundamental science, quantum information processing, and sensing.

quant-ph↗

arXiv2023

Universal control of a bosonic mode via drive-activated native cubic interactions

Linear bosonic modes offer a hardware-efficient alternative for quantum information processing but require access to some nonlinearity for universal control. The lack of nonlinearity in photonics has led to encoded measurement-based quantum computing, which rely on linear operations but requires access to resourceful ('nonlinear') quantum states, such as cubic phase states. In contrast, superconducting microwave circuits offer engineerable nonlinearities but suffer from static Kerr nonlinearity. Here, we demonstrate universal control of a bosonic mode composed of a superconducting nonlinear asymmetric inductive element (SNAIL) resonator, enabled by native nonlinearities in the SNAIL element. We suppress static nonlinearities by operating the SNAIL in the vicinity of its Kerr-free point and dynamically activate nonlinearities up to third order by fast flux pulses. We experimentally realize a universal set of generalized squeezing operations, as well as the cubic phase gate, and exploit them to deterministically prepare a cubic phase state in 60 ns. Our results initiate the experimental field of universal continuous-variables quantum computing.

quant-ph↗

arXiv2022

Experimental realization of deterministic and selective photon addition in a bosonic mode assisted by an ancillary qubit

Bosonic quantum error correcting codes are primarily designed to protect against single-photon loss. To correct for this type of error, one can encode the logical qubit in code spaces with a definite photon parity, such as cat codes or binomial codes. Error correction requires a recovery operation that maps the error states -- which have opposite parity -- back onto the code states. Here, we realize a collection of photon-number-selective, simultaneous photon addition operations on a bosonic mode, a microwave cavity, assisted by a superconducting qubit. These operations are implemented as two-photon transitions that excite the cavity and the qubit at the same time. The additional degree of freedom of the qubit makes it possible to implement a coherent, unidirectional mapping between spaces of opposite photon parity. We present the successful experimental implementation of the drives and the phase control they enable on superpositions of Fock states. The presented technique, when supplemented with qubit reset, is suitable for autonomous quantum error correction in bosonic systems, and, more generally, opens the possibility to realize a range of non-unitary transformations on a bosonic mode.

quant-ph↗

arXiv2015

Selective nonresonant excitation of vibrational modes in suspended graphene via vibron-plasmon interaction

We theoretically study a doped graphene ribbon suspended over a trench and subject to an ac-electrical field polarized perpendicularly to the graphene plane. In such a system, the external ac-field is coupled to the relatively slow mechanical vibrations via plasmonic oscillations in the isolated graphene sheet. We show that the electrical field generates an effective pumping of the mechanical modes. It is demonstrated that in the case of underdamped plasma oscillation, a peculiar kind of geometrical resonance of the mechanical and plasma oscillations appear. Namely the efficiency of pumping significantly increases when the wave number of the mechanical mode is in close agreement with the wave number of the plasma waves. The intensity of the pumping increases with the wave number of the mode. This phenomenon allows selective actuation of different mechanical modes although the driving field is homogeneous.

cond-mat.mes-hall↗

arXiv2014

Nonresonant high frequency excitation of mechanical vibrations in graphene based nanoresonator

We theoretically analyse the dynamics of a suspended graphene membrane which is in tunnel contact with grounded metallic electrodes and subjected to ac-electrostatic potential induced by a gate electrode. It is shown that for such system the retardation effects in the electronic subsystem generate an effective pumping for the relatively slow mechanical vibrations if the driving frequency exceeds the inverse charge relax- ation time. Under this condition there is a critical value of the driving voltage ampli- tude above which the pumping overcomes the intrinsic damping of the mechanical resonator leading to a mechanical instability. This nonresonant instability is saturated by nonlinear damping and the system exhibits self-sustained oscillations of relatively large amplitude.

cond-mat.mes-hall↗