arXiv subjects

Michael Trupke

Publications and source records attributed to Michael Trupke.

At least 19 recordsLinked to original sources

arXiv2026

Exploiting ionization dynamics in the nitrogen vacancy center for rapid, high-contrast spin and charge state initialization

We propose and experimentally demonstrate a method to strongly increase the sensitivity of spin measurements on nitrogen-vacancy (NV) centers in diamond, which can be readily implemented in existing quantum sensing experiments. While charge state transitions of this defect are generally considered a parasitic effect to be avoided, we show here that these can be used to significantly increase the NV center's spin contrast, a key quantity for high sensitivity magnetometry and high fidelity state readout. The protocol consists of a two-step procedure, in which the charge state of the defect is first purified by a strong laser pulse, followed by weak illumination to obtain high spin polarization. We observe a relative improvement of the readout contrast by 17 %, and infer a reduction of the initialization error of more than 50 %. The contrast enhancement is accompanied by a beneficial increase of the readout signal. For long sequence durations, typically encountered in high-resolution magnetometry, a measurement speedup by a factor of >1.5 is extracted, and we find that the technique is beneficial for sequences of any duration. Additionally, our findings give detailed insight into the charge and spin polarization dynamics of the NV center, and provide actionable insights for direct optical, spin-to-charge, and electrical readout of solid-state spin centres.

quant-ph↗

arXiv2025

Strain-enabled control of the vanadium qudit in silicon carbide

Vanadium in silicon carbide is a promising spin photon interface candidate with optical transitions in the telecom range and a long lived electron spin, hosted in an advanced semiconductor platform. In this detailed investigation of the defect's 16-dimensional ground state spin manifold at millikelvin temperatures, a wide range of previously unreported transitions are observed which are accurately described using a theoretical model that includes strain. Using a superconducting microcoil we achieve Rabi frequencies exceeding 20 MHz and perform the first coherent manipulation of a direct hyperfine transition. These insights further underscore the defect's potential for strain engineering and sensing, as well as for fault-tolerant qudit encoding.

quant-ph↗

arXiv2024

Modelling magnetically-levitated superconducting ellipsoids, cylinders and cuboids for quantum magnetomechanics

We theoretically investigate the properties of magnetically-levitated superconducting rotors confined in anti-Helmholtz traps, for application in magnetomechanical experiments. We study both the translational modes and a librational mode. The librational mode gives an additional degree of freedom that levitated spheres do not have access to. We compare rotors of different shapes: ellipsoids, cylinders and cuboids. We find that the stable orientations of the rotors depend on the rotors' aspect ratios.

physics.app-ph↗

arXiv2024

Microelectronic readout of a diamond quantum sensor

Quantum sensors based on the nitrogen-vacancy (NV) centre in diamond are rapidly advancing from scientific exploration towards the first generation of commercial applications. While significant progress has been made in developing suitable methods for the manipulation of the NV centre spin state, the detection of the defect luminescence has so far limited the performance of miniaturized sensor architectures. The recent development of photoelectric detection of the NV centre's spin state offers a path to circumvent these limitations, but has to-date required research-grade low current amplifiers to detect the picoampere-scale currents obtained from these systems. Here we report on the photoelectric detection of magnetic resonance (PDMR) with NV ensembles using a complementary metal-oxide semiconductor (CMOS) device. The integrated circuit delivers a digitized output of the diamond sensor with low noise and 50 femtoampere resolution. This integration provides the last missing component on the path to a compact, diamond-based quantum sensor. The device is suited for continuous wave (CW) as well as pulsed operation. We demonstrate its functionality with DC and AC magnetometry up to several megahertz, coherent spin rotation and multi-axial decoupling sequences for quantum sensing.

quant-ph↗

arXiv2024

Quantum communication networks with defects in silicon carbide

Quantum communication promises unprecedented capabilities enabled by the transmission of quantum states of light. However, current implementations face severe distance limitations due to photon loss. Silicon carbide (SiC) defects have emerged as a promising quantum device platform, offering strong optical transitions, long spin coherence lifetimes and the opportunity for integration with semiconductor devices. Some defects with optical transitions in the telecom range have been identified, allowing to interface with fiber networks without the need for wavelength conversion. These unique properties make SiC an attractive platform for the implementation of quantum nodes for quantum communication networks. We provide an overview of the most prominent defects in SiC and their implementation in spin-photon interfaces. Furthermore, we model an exemplary, memory-enhanced quantum communication protocol in order to extract the parameters required to surpass a direct point-to-point link performance. Based on these insights, we summarize the key steps required towards the deployment of SiC devices in large-scale quantum communication networks.

quant-ph↗

arXiv2024

Remote sensing of a levitated superconductor with a flux-tunable microwave cavity

We present a cavity-electromechanical system comprising a superconducting quantum interference device which is embedded in a microwave resonator and coupled via a pick-up loop to a 6 $\mu$g magnetically-levitated superconducting sphere. The motion of the sphere in the magnetic trap induces a frequency shift in the SQUID-cavity system. We use microwave spectroscopy to characterize the system, and we demonstrate that the electromechanical interaction is tunable. The measured displacement sensitivity of $10^{-7} \, \mathrm{m} / \sqrt{\mathrm{Hz}}$, defines a path towards ground-state cooling of levitated particles with Planck-scale masses at millikelvin environment temperatures.

quant-ph↗

arXiv2023

Ultra-narrow inhomogeneous spectral distribution of telecom-wavelength vanadium centres in isotopically-enriched silicon carbide

Spin-active quantum emitters have emerged as a leading platform for quantum technologies. However, one of their major limitations is the large spread in optical emission frequencies, which typically extends over tens of GHz. Here, we investigate single V4+ vanadium centres in 4H-SiC, which feature telecom-wavelength emission and a coherent S=1/2 spin state. We perform spectroscopy on single emitters and report the observation of spin-dependent optical transitions, a key requirement for spin-photon interfaces. By engineering the isotopic composition of the SiC matrix, we reduce the inhomogeneous spectral distribution of different emitters down to 100 MHz, significantly smaller than any other single quantum emitter. Additionally, we tailor the dopant concentration to stabilise the telecom-wavelength V4+ charge state, thereby extending its lifetime by at least two orders of magnitude. These results bolster the prospects for single V emitters in SiC as material nodes in scalable telecom quantum networks.

quant-ph↗

arXiv2022

High-Q magnetic levitation and control of superconducting microspheres at millikelvin temperatures

We report the levitation of a superconducting lead-tin sphere with 100 micrometer diameter (corresponding to a mass of 5.6 micrograms) in a static magnetic trap formed by two coils in an anti-Helmholtz configuration, with adjustable resonance frequencies up to 240 hertz. The center-of-mass motion of the sphere is monitored magnetically using a dc superconducting quantum interference device as well as optically and exhibits quality factors of up to 2.6e7. We also demonstrate 3D magnetic feedback control of the sphere's motion. The setup is housed in a dilution refrigerator operating at 15 millikelvin. By implementing a cryogenic vibration isolation system we can attenuate environmental vibrations at 200 hertz by approximately seven orders of magnitude. The combination of low temperature, large mass and high quality factor as well as adjustable resonance frequencies provides a promising platform for testing quantum physics in previously unexplored regimes with high mass and long coherence times.

quant-ph↗

arXiv2022

Nuclear Spin Quantum Memory in Silicon Carbide

Transition metal (TM) defects in silicon carbide (SiC) are a promising platform for applications in quantum technology. Some TM defects, e.g. vanadium, emit in one of the telecom bands, but the large ground state hyperfine manifold poses a problem for applications which require pure quantum states. We develop a driven, dissipative protocol to polarize the nuclear spin, based on a rigorous theoretical model of the defect. We further show that nuclear-spin polarization enables the use of well-known methods for initialization and long-time coherent storage of quantum states. The proposed nuclear-spin preparation protocol thus marks the first step towards an all-optically controlled integrated platform for quantum technology with TM defects in SiC.

cond-mat.mes-hall↗

arXiv2021

Hyperfine-mediated transitions between electronic spin-1/2 levels of transition metal defects in SiC

Transition metal defects in SiC give rise to localized electronic states that can be optically addressed in the telecom range in an industrially mature semiconductor platform. This has led to intense scrutiny of the spin and optical properties of these defect centers. For spin-1/2 defects, a combination of the defect symmetry and the strong spin-orbit coupling may restrict the allowed spin transitions, giving rise to defect spins that are long lived, but hard to address via microwave spin manipulation. Here, we show via analytical and numerical results that the presence of a central nuclear spin can lead to a non-trivial mixing of electronic spin states, while preserving the defect symmetry. The interplay between a small applied magnetic field and hyperfine coupling opens up magnetic microwave transitions that are forbidden in the absence of hyperfine coupling, enabling efficient manipulation of the electronic spin. We also find that an electric microwave field parallel to the c-axis can be used to manipulate the electronic spin via modulation of the relative strength of the dipolar hyperfine term.

quant-ph↗

arXiv2021

High finesse microcavities in the optical telecom O-band

Optical microcavities allow to strongly confine light in small mode volumes and with long photon lifetimes. This confinement significantly enhances the interaction between light and matter inside the cavity, with applications such as optical trapping and cooling of nanoparticles, single-photon emission enhancement, quantum information processing, and sensing. For many applications, open resonators with direct access to the mode volume are necessary. Here we report on a scalable, open-access optical microcavity platform with mode volumes < 30 $λ^3$ and finesse approaching $5x10^5$. This result significantly exceeds the highest optical enhancement factors achieved to date for Fabry-Pérot cavities. The platform provides a building block for high-performance quantum devices relying on strong light-matter interaction.

quant-ph↗

arXiv2021

Room-temperature control and electrical readout of individual nitrogen-vacancy nuclear spins

Nuclear spins in semiconductors are leading candidates for quantum technologies, including quantum computation, communication, and sensing. Nuclear spins in diamond are particularly attractive due to their extremely long coherence lifetime. With the nitrogen-vacancy (NV) centre, such nuclear qubits benefit from an auxiliary electronic qubit, which has enabled entanglement mediated by photonic links. The transport of quantum information by the electron itself, via controlled transfer to an adjacent centre or via the dipolar interaction, would enable even faster and smaller processors, but optical readout of arrays of such nodes presents daunting challenges due to the required sub-diffraction inter-site distances. Here, we demonstrate the electrical readout of a basic unit of such systems - a single 14N nuclear spin coupled to the NV electron. Our results provide the key ingredients for quantum gate operations and electrical readout of nuclear qubit registers, in a manner compatible with nanoscale electrode structures. This demonstration is therefore a milestone towards large-scale diamond quantum devices with semiconductor scalability.

cond-mat.mes-hall↗

arXiv2020

Levitation of superconducting micro-rings for quantum magnetomechanics

Levitation of superconductors is becoming an important building block in quantum technologies, particularly in the rising field of magnetomechanics. In most of the theoretical proposals and experiments, solid geometries such as spheres are considered for the levitator. Here we demonstrate that replacing them by superconducting rings brings two important advantages: Firstly, the forces acting on the ring remain comparable to those expected for solid objects, while the mass of the superconductor is greatly reduced. In turn, this reduction increases the achievable trap frequency. Secondly, the flux trapped in the ring by in-field cooling yields an additional degree of control for the system. We construct a general theoretical framework with which we obtain analytical formulations for a superconducting ring levitating in an anti-Helmholtz quadrupole field and a dipole field, for both zero-field and in-field cooling. The positions and the trapping frequencies of the levitated rings are analytically found as a function of the parameters of the system and the field applied during the cooling process. Unlike what is commonly observed in bulk superconductors, lateral and rotational stability are not granted for this idealized geometry. We therefore discuss the requirements for simple superconducting structures to achieve stability in all degrees of freedom.

cond-mat.supr-con↗

arXiv2018

Scalable spin-photon entanglement by time-to-polarization conversion

Spin-photon interfaces are strong candidates for building blocks of future quantum networks and quantum computers. Several systems currently under examination present promising features, but none of them yet fulfil all requirements for these aims. A particularly attractive strategy for the realization of these applications is the creation of strings of entangled photons, where quantum correlations among the photons are mediated by operations on the spin of the emitter. Here, we demonstrate for the first time the creation of spin-photon entanglement within the fundamental unit of a novel, scalable protocol based on time-to-polarization conversion. This principle allows us to bypass many of the imperfections of currently available photon sources and can therefore be utilized with a large variety of emitters. We execute the protocol using a nitrogen-vacancy centre in diamond, which possesses a long coherence lifetime and multiple spin degrees of freedom, thereby offering an outlook towards the creation of large entangled states.

quant-ph↗

arXiv2018

Proposal for a Quantum Test of the Weak Equivalence Principle with Entangled Atomic Species

We propose an experiment to test the Weak Equivalence Principle (WEP) with a test mass consisting of two entangled atoms of different species. In the proposed experiment, a coherent measurement of the differential gravity acceleration between the two atomic species is considered, by entangling two atom interferometers operating on the two species. The entanglement between the two atoms is heralded at the initial beam splitter of the interferometers through the detection of a single photon emitted by either of the atoms, together with the impossibility of distinguishing which atom emitted the photon. In contrast to current and proposed tests of the WEP, our proposal explores the validity of the WEP in a regime where the two particles involved in the differential gravity acceleration measurement are not classically independent, but entangled. We propose an experimental implementation using $^{85}$Rb and $^{87}$Rb atoms entangled by a vacuum stimulated rapid adiabatic passage protocol implemented in a high finesse optical cavity. We show that an accuracy below $10^{-7}$ on the Eötvös parameter can be achieved.

gr-qc↗

arXiv2017

Nanoparticle detection in an open-access silicon microcavity

We report on the detection of free nanoparticles in a micromachined, open-access Fabry-Pérot microcavity. With a mirror separation of $130\,μ$m, a radius of curvature of $1.3\,$mm, and a beam waist of $12\,μ$m, the mode volume of our symmetric infrared cavity is smaller than $15\,$pL. The small beam waist, together with a finesse exceeding 34,000, enables the detection of nano-scale dielectric particles in high vacuum. This device allows monitoring of the motion of individual $150\,$nm radius silica nanospheres in real time. We observe strong coupling between the particles and the cavity field, a precondition for optomechanical control. We discuss the prospects for optical cooling and detection of dielectric particles smaller than $10\,$nm in radius and $1\times10^7\,$amu in mass.

quant-ph↗

arXiv2017

High-Fidelity Spin Measurement on the Nitrogen-Vacancy Center

Nitrogen-vacancy (NV) centers in diamond are versatile candidates for many quantum information processing tasks, ranging from quantum imaging and sensing through to quantum communication and fault-tolerant quantum computers. Critical to almost every potential application is an efficient mechanism for the high fidelity readout of the state of the electronic and nuclear spins. Typically such readout has been achieved through an optically resonant fluorescence measurement, but the presence of decay through a meta-stable state will limit its efficiency to the order of 99%. While this is good enough for many applications, it is insufficient for large scale quantum networks and fault-tolerant computational tasks. Here we explore an alternative approach based on dipole induced transparency (state-dependent reflection) in an NV center cavity QED system, using the most recent knowledge of the NV center's parameters to determine its feasibility, including the decay channels through the meta-stable subspace and photon ionization. We find that single-shot measurements above fault-tolerant thresholds should be available in the strong coupling regime for a wide range of cavity-center cooperativities, using a majority voting approach utilizing single photon detection. Furthermore, extremely high fidelity measurements are possible using weak optical pulses.

quant-ph↗

arXiv2017

Solid-state electron spin lifetime limited by phononic vacuum modes

Longitudinal relaxation is the process by which an excited spin ensemble decays into its thermal equilibrium with the environment. In solid-state spin systems relaxation into the phonon bath usually dominates over the coupling to the electromagnetic vacuum. In the quantum limit the spin lifetime is determined by phononic vacuum fluctuations. However, this limit was not observed in previous studies due to thermal phonon contributions or phonon-bottleneck processes. Here we use a dispersive detection scheme based on cavity quantum electrodynamics (cQED) to observe this quantum limit of spin relaxation of the negatively charged nitrogen vacancy ($\mathrm{NV}^-$) centre in diamond. Diamond possesses high thermal conductivity even at low temperatures, which eliminates phonon-bottleneck processes. We observe exceptionally long longitudinal relaxation times $T_1$ of up to 8h. To understand the fundamental mechanism of spin-phonon coupling in this system we develop a theoretical model and calculate the relaxation time ab initio. The calculations confirm that the low phononic density of states at the $\mathrm{NV}^-$ transition frequency enables the spin polarization to survive over macroscopic timescales.

cond-mat.mes-hall↗