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The realization of on-chip quantum interfaces between flying photons and solid-state spins is a key building block for quantum-information processors, enabling, e.g., distributed quantum computing, where remote quantum registers are interconnected by flying photons. Self-assembled quantum dots integrated into nanostructures are one of the most promising systems for such an endeavor thanks to their near-unity photon-emitter coupling and fast spontaneous emission rate. Here we demonstrate high-fidelity on-chip entanglement between an incoming photon and a stationary quantum-dot hole spin qubit. The entanglement is induced by sequential scattering of the time-bin encoded photon interleaved with active spin control within a microsecond, two orders of magnitude faster than those achieved in other solid-state platforms. Conditioning on the detection of a reflected photon renders the entanglement fidelity immune to the spectral wandering of the emitter. These results represent a major step towards realizing a quantum node capable of interchanging information with flying photons and on-chip quantum logic, as required for quantum networks and quantum repeaters.

Quantum dot molecules (QDMs) are one of the few quantum light sources that promise deterministic generation of one- and two-dimensional photonic graph states. The proposed protocols rely on coherent excitation of the tunnel-coupled and spatially indirect exciton states. Here, we demonstrate power-dependent Rabi oscillations of direct excitons, spatially indirect excitons, and excitons with a hybridized electron wave function. An off-resonant detection technique based on phonon-mediated state transfer allows for spectrally filtered detection under resonant excitation. Applying a gate voltage to the QDM-device enables a continuous transition between direct and indirect excitons and, thereby, control of the overlap of the electron and hole wave function. This does not only vary the Rabi frequency of the investigated transition by a factor of $\approx3$, but also allows to optimize graph state generation in terms of optical pulse power and reduction of radiative lifetimes., Comment: 6 pages, 3 figures

Semiconductor quantum dot molecules are considered as promising candidates for quantum technological applications due to their wide tunability of optical properties and coverage of different energy scales associated with charge and spin physics. While previous works have studied the tunnel-coupling of the different excitonic charge complexes shared by the two quantum dots by conventional optical spectroscopy, we here report on the first demonstration of a coherently controlled inter-dot tunnel-coupling focusing on the quantum coherence of the optically active trion transitions. We employ ultrafast four-wave mixing spectroscopy to resonantly generate a quantum coherence in one trion complex, transfer it to and probe it in another trion configuration. With the help of theoretical modelling on different levels of complexity we give an instructive explanation of the underlying coupling mechanism and dynamical processes.

The interaction between photons and a single two-level atom constitutes a fundamental paradigm in quantum physics. The nonlinearity provided by the atom leads to a strong dependence of the light–matter interface on the number of photons interacting with the two-level system within its emission lifetime. This nonlinearity unveils strongly correlated quasiparticles known as photon bound states, giving rise to key physical processes such as stimulated emission and soliton propagation. Although signatures consistent with the existence of photon bound states have been measured in strongly interacting Rydberg gases, their hallmark excitation-number-dependent dispersion and propagation velocity have not yet been observed. Here we report the direct observation of a photon-number-dependent time delay in the scattering off a single artificial atom—a semiconductor quantum dot coupled to an optical cavity. By scattering a weak coherent pulse off the cavity–quantum electrodynamics system and measuring the time-dependent output power and correlation functions, we show that single photons and two- and three-photon bound states incur different time delays, becoming shorter for higher photon numbers. This reduced time delay is a fingerprint of stimulated emission, where the arrival of two photons within the lifetime of an emitter causes one photon to stimulate the emission of another.

Scalable photonic quantum computing architectures pose stringent requirements on photonic processing devices. The needs for low-loss high-speed reconfigurable circuits and near-deterministic resource state generators are some of the most challenging requirements. Here, we develop an integrated photonic platform based on thin-film lithium niobate and interface it with deterministic solid-state single-photon sources based on quantum dots in nanophotonic waveguides. The generated photons are processed with low-loss circuits programmable at speeds of several gigahertz. We realize a variety of key photonic quantum information processing functionalities with the high-speed circuits, including on-chip quantum interference, photon demultiplexing, and reprogrammability of a four-mode universal photonic circuit. These results show a promising path forward for scalable photonic quantum technologies by merging integrated photonics with solid-state deterministic photon sources in a heterogeneous approach to scaling up.

We investigate experimentally the capacitive coupling between a two-electron singlet-triplet spin qubit and flying electrons propagating in quantum Hall edge channels. After calibration of the spin qubit detector, we assess its charge sensibility and demonstrate experimentally the detection of less than five flying electrons with average measurement. This experiment demonstrates that the spin qubit is an ultrasensitive and fast charge detector with the perspective of a future single shot-detection of a single flying electron. This work opens the route toward quantum electron optics experiments at the single electron level in semiconductor circuits.

We report a method for integrating GaAs waveguide circuits containing self-assembled quantum dots on a Si/SiO2 wafer, using die-to-wafer bonding. The large refractive-index contrast between GaAs and SiO2 enables fabricating single-mode waveguides without compromising the photon-emitter coupling. Anti-bunched emission from individual quantum dots is observed, along with a waveguide propagation loss

We propose and demonstrate complete spin state readout of a two-electron system in a double quantum dot probed by an electrometer. The protocol is based on repetitive single shot measurements using Pauli spin blockade and our ability to tune on fast timescales the detuning and the interdot tunnel coupling between the GHz and sub-Hz regime. A sequence of three distinct manipulations and measurements allows establishing if the spins are in S, Tzero, Tplus or Tminus state. This work points at a procedure to reduce the overhead for spin readout, an important challenge for scaling up spin qubit platforms., 11 pages, 7 figures

Quantum dots are recognized as a suitable platform for studying thermodynamic phenomena involving single electronic charges and spins in nano-scale devices. However, such a thermodynamic system is usually driven by electron reservoirs at different temperatures, not by a lattice temperature gradient. We report on experimental observations of charge-spin cooperative dynamics in transitions of two-electron spin states in a GaAs double quantum dot located in a non-equilibrium phonon environment. Enhancements in the spin-flip processes are observed, originating from phonon excitation combined with the spin-orbit interaction. In addition, due to the spatial gradient of phonon density between the dots, the spin-flip rate during an inter-dot electron tunnel from a hot to a cold dot is more enhanced than in the other direction, resulting in accumulation of parallel spin states in the double dot.

Recent demonstrations using electron spins stored in quantum dots array as qubits are promising for developing a scalable quantum computing platform. An ongoing effort is therefore aiming at the precise control of the quantum dots parameters in larger and larger arrays which represents a complex challenge. Partitioning of the system with the help of the inter-dot tunnel barriers can lead to a simplification for tuning and offers a protection against unwanted charge displacement. In a triple quantum dot system, we demonstrate a nanosecond control of the inter-dot tunnel rate permitting to reach the two extreme regimes, large GHz tunnel coupling and sub-Hz isolation between adjacent dots. We use this novel development to isolate a sub part of the array while performing charge displacement and readout in the rest of the system. The degree of control over the tunnel coupling achieved in a unit cell should motivate future protocol development for tuning, manipulation and readout including this capability., 10 pages, 8 figures

Combining the capabilities of gate defined quantum transport devices in GaAs-based heterostructures and of optically addressed self-assembled quantum dots could open broad perspectives for new devices and functionalities. For example, interfacing stationary solid-state qubits with photonic quantum states would open a new pathway towards the realization of a quantum network with extended quantum processing capacity in each node. While gated devices allow very flexible confinement of electrons or holes, the confinement of excitons without some element of self-assembly is much harder. To address this limitation, we introduce a technique to realize exciton traps in quantum wells via local electric fields by thinning a heterostructure down to a 220 nm thick membrane. We show that mobilities over $1 \times 10^{6}$ cm$^{2}$V$^{-1}$s$^{-1}$ can be retained and that quantum point contacts and Coulomb oscillations can be observed on this structure, which implies that the thinning does not compromise the heterostructure quality. Furthermore, the local lowering of the exciton energy via the quantum-confined Stark effect is confirmed, thus forming exciton traps. These results lay the technological foundations for devices like single photon sources, spin photon interfaces and eventually quantum network nodes in GaAs quantum wells, realized entirely with a top-down fabrication process., v2: added missing acknowledgement. v3: fixed typos in acknolwedgement

The ability to extend the time scale of the coherent optical response from large ensembles of quantum emitters is highly appealing for applications in quantum information devices. In semiconductor nanostructures, spin degrees of freedom can be used as auxiliary, powerful tools to modify the coherent optical dynamics. Here, we apply this approach to negatively charged (In,Ga)As/GaAs self-assembled quantum dots which are considered as excellent quantum emitters with robust optical coherence and high bandwidth. We study three-pulse spin-dependent photon echoes subject to moderate transverse magnetic fields up to 1 T. We demonstrate that the timescale of coherent optical response can be extended by at least an order of magnitude by the field. Without magnetic field, the photon echo decays with T2 = 0.45 ns which is determined by the radiative lifetime of trions T1 = 0.26 ns. In the presence of the transverse magnetic field, the decay of the photon echo signal is given by spin dephasing time of the ensemble of resident electrons T2,e ∼ 4 ns. We demonstrate that the non-zero transverse g-factor of the heavy holes in the trion state plays a crucial role in the temporal evolution and magnetic field dependence of the long-lived photon echo signal., Communications physics;Bd 5, 2022, H. 1, Artikel-ID 144

In a radiative Auger process, an excited electron relaxes by concomitant emission of a redshifted photon and energy transfer to another electron. Measuring radiative Auger processes in a quantum dot with single-photon resolution enables determination of the energy of single-electron levels as well as their lifetimes.In a multi-electron atom, an excited electron can decay by emitting a photon. Typically, the leftover electrons are in their ground state. In a radiative Auger process, the leftover electrons are in an excited state and a redshifted photon is created(1-4). In a semiconductor quantum dot, radiative Auger is predicted for charged excitons(5). Here we report the observation of radiative Auger on trions in single quantum dots. For a trion, a photon is created on electron-hole recombination, leaving behind a single electron. The radiative Auger process promotes this additional (Auger) electron to a higher shell of the quantum dot. We show that the radiative Auger effect is a powerful probe of this single electron: the energy separations between the resonance fluorescence and the radiative Auger emission directly measure the single-particle splittings of the electronic states in the quantum dot with high precision. In semiconductors, these single-particle splittings are otherwise hard to access by optical means as particles are excited typically in pairs, as excitons. After the radiative Auger emission, the Auger carrier relaxes back to the lowest shell. Going beyond the original theoretical proposals, we show how applying quantum optics techniques to the radiative Auger photons gives access to the single-electron dynamics, notably relaxation and tunnelling. This is also hard to access by optical means: even for quasi-resonantp-shell excitation, electron relaxation takes place in the presence of a hole, complicating the relaxation dynamics. The radiative Auger effect can be exploited in other semiconductor nanostructures and quantum emitters in the solid state to determine the energy levels and the dynamics of a single carrier.

Auger recombination is a nonradiative process, where the recombination energy of an electron-hole pair is transferred to a third charge carrier. It is a common effect in colloidal quantum dots that quenches the radiative emission with an Auger recombination time below nanoseconds. In self-assembled QDs, the Auger recombination has been observed with a much longer recombination time on the order of microseconds. Here, we use two-color laser excitation on the exciton and trion transition in resonance fluorescence on a single self-assembled quantum dot to monitor in real-time single quantum events of the Auger process. Full counting statistics on the random telegraph signal give access to the cumulants and demonstrate the tunability of the Fano factor from a Poissonian to a sub-Poissonian distribution by Auger-mediated electron emission from the dot. Therefore, the Auger process can be used to tune optically the charge carrier occupation of the dot by the incident laser intensity, independently from the electron tunneling from the reservoir by the gate voltage. Our findings are not only highly relevant for the understanding of the Auger process but also demonstrate the perspective of the Auger effect for controlling precisely the charge state in a quantum system by optical means.

Photonic quantum technology provides a viable route to quantum communication

7 pags., 3 figs., Single photons role in the development of quantum science and technology. They can carry quantum information over extended distances to act as the backbone of a future quantum internet and can be manipulated in advanced photonic circuits, enabling scalable photonic quantum computing. However, more sophisticated devices and protocols need access to multi-photon states with particular forms of entanglement. Efficient light–matter interfaces offer a route to reliably generating these entangled resource states. Here we utilize the efficient and coherent coupling of a single quantum emitter to a nanophotonic waveguide to realize a quantum nonlinear interaction between single-photon wavepackets. We demonstrate the control of a photon using a second photon mediated by the quantum emitter. The dynamical response of the two-photon interaction is experimentally unravelled and reveals quantum correlations controlled by the pulse duration. Further development of this platform work, which constitutes a new research frontier in quantum optics, will enable the tailoring of complex photonic quantum resource states., We acknowledge funding from the Danish National Research Foundation (Center of Excellence ‘Hy-Q,’ grant number DNRF139). This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 824140 (TOCHA, H2020-FETPROACT-01-2018). A.D.W. and A.L. gratefully acknowledge financial support from Deutsche Forschungsgemeinschaft (DFG) (TRR 160 and LU2051/1-1) and the grants QR.X KIS6QK4001 and DFH/UFA CDFA-05-06. Work in Madrid is funded by the Spanish project PGC2018-094792-B-I00 (MCIU/AEI/ FEDER, UE), CSIC Research Platform on Quantum Technologies PTI-001 and Proyecto Sinergico CAM 2020 Y2020/TCS-6545 (NanoQuCo-CM). T.R. further acknowledges support from the Juan de la Cierva fellowship IJC2019-040260-I.

We present the heterogeneous integration of GaAs membranes with embedded quantum dots on a Silicon substrate, based on die-to-die bonding method. We demonstrate light transmission in GaAs nanobeam waveguides and emission from individual quantum emitters.

The electron tunneling rates between a two-dimensional electron gas (2DEG) and self-assembled InAs quantum dots are studied by applying a magnetic field perpendicular to the tunneling direction. For both the ground and the first excited states, the tunneling rate can be modified by a magnetic field. The field dependence of both the s and p state tunneling rates can be explained with a model, based on momentum matching between the Fermi surface of the 2DEG and the wave function of the quantum dots in momentum space. The results, together with the comparison between charging and discharging rates, provide insight into the filling sequence of the p-state electrons. Published under an exclusive license by AIP Publishing.

On-demand single-photon sources emitting pure and indistinguishable photons at the telecommunication wavelength are a critical asset towards the deployment of fiber-based quantum networks. Indeed, single photons may serve as flying qubits, allowing communication of quantum information over long distances. Self-assembled InAs quantum dots embedded in GaAs constitute an excellent nearly deterministic source of high quality single photons, but the vast majority of sources operate in the 900-950 nm wavelength range, precluding their adoption in a quantum network. Here, we present a quantum frequency conversion scheme for converting single photons from quantum dots to the telecommunication C band, around 1550 nm, achieving 40.8% end-to-end efficiency, while maintaining both high purity and a high degree of indistinguishability during conversion with measured values of $g^{(2)}(0)=2.4\%$ and $V^{\text{corr}}=94.8\%$, respectively., Comment: 7 pages, 4 figures

International audience; Electron flying qubits are envisioned as potential information link within a quantum computer, but also promise -- alike photonic approaches -- a self-standing quantum processing unit. In contrast to its photonic counterpart, electron-quantum-optics implementations are subject to Coulomb interaction, which provide a direct route to entangle the orbital or spin degree of freedom. However, the controlled interaction of flying electrons at the single particle level has not yet been established experimentally. Here we report antibunching of a pair of single electrons that is synchronously shuttled through a circuit of coupled quantum rails by means of a surface acoustic wave. The in-flight partitioning process exhibits a reciprocal gating effect which allows us to ascribe the observed repulsion predominantly to Coulomb interaction. Our single-shot experiment marks an important milestone on the route to realise a controlled-phase gate for in-flight quantum manipulations.

We realize a quantum photonic circuit enabling the resonant excitation of multiple quantum emitters. Using independent electrical control, we demonstrate quantum interference between two embedded quantum dots in a single device. Our result represents a crucial step towards on-chip multi-photon generation for quantum information applications.

Electron spins in gate-defined quantum dots (QDs) formed in semiconductor quantum wells (QWs) are promising stationary qubits for implementing large-scale quantum networks in a scalable manner. One key ingredient for such a network is an efficient photon–spin interface that converts any polarization state of a flying photonic qubit to the corresponding spins state of the electron in gate-defined QDs. A bull’s-eye cavity is an optical cavity structure that can enhance the photon absorption of an embedded gate-defined QD without polarization dependence. In this paper, we report the successful fabrication of air-bridge bull’s-eye cavities with metal electrodes and demonstrate the nearly polarization-independent optical absorption of a GaAs QW embedded in the cavities. This work marks an important step toward realizing an efficient photon–spin interface using gate-defined QDs.

The authors report on a mechanism of strong enhancement of the band Land\'e parameter $q$ due to in-plane confinement of holes and the valence-band warping. This explains the surprisingly large in-plane hole $g$ factor in symmetric self-assembled (In,Ga)As/GaAs quantum dots with $D2d$ symmetry as revealed by coherent optical spectroscopy. The proposed mechanism results in uniform magnetic field induced optical anisotropy for the entire quantum dot ensemble, which is a prerequisite for the realization of spin quantum memories and spin-photon entanglement in the ensemble.

International audience; The ability to shuttle coherently individual electron spins in arrays of quantum dots is a key procedure for the development of scalable quantum information platforms. It allows the use of sparsely populated electron spin arrays, envisioned to efficiently tackle the one-and two-qubit gate challenges. When the electrons are displaced in an array, they are exposed to site-dependent environment interactions such as hyperfine coupling with substrate nuclear spins. Here, we demonstrate that the electron multidirectional displacement in a 3 × 3 array of tunnel-coupled quantum dots enhances the spin-coherence time via the motional narrowing phenomenon. More specifically, up to ten charge configurations are explored by the electrons to study the impact of the displacement on spin dynamics. An increase of the coherence time by a factor up to 10 is observed in the case of fast and repetitive displacement. A simple model quantitatively captures the physical mechanism underlying this enhancement of the spin-coherence time induced by displacement. The implications on spin-coherence properties during the electron displacement are discussed in the context of large-scale quantum circuits.

The electron transfer dynamics between self-assembled quantum dots and their environment are measured under nonequilibrium conditions by time-dependent capacitance spectroscopy. The quantum dots are embedded in a wide spacer, which inhibits elastic tunneling to or from the reservoirs. At certain bias voltages, electron capture and emission are both significant. A rate equation model is used to determine the corresponding transfer rates and the average occupation numbers of the dots as a function of the bias voltage.

Neodymium sulphide (Nd2S3) belongs to the exciting class of rare earth sulphides (RES) and is projected to have a serious potential in a wide spectrum of application either in pure form or as dopant. We demonstrate a facile and first growth of Nd2S3 thin films via metal–organic chemical vapour deposition (MOCVD) at moderate process conditions using two new Nd precursors, namely tris(N,N′-diisopropyl-2-dimethylamido-guanidinato)Nd(III) and tris(N,N′-diisopropyl-acetamidinato)Nd(III). The promising thermal properties and suitable reactivity of both Nd precursors towards elemental sulphur enabled the formation of high purity γ-Nd2S3. While the process temperature for film growth ranged from 400 °C to 600 °C, the films were crystalline above 500 °C. We also demonstrate that the as-deposited γ-Nd2S3 are luminescent, with the optical bandgap ranging from 2.3 eV to 2.5 eV. The process circumvents post-deposition treatments such as sulfurisation to fabricate the desired Nd2S3, which paves the way for large scale synthesis and also opens up new avenues for exploring the potential of this class of materials with properties for functional applications.

In the quest for large-scale quantum computing, networked quantum computers offer a natural path towards scalability. Now that nearest neighbor entanglement has been demonstrated for electron spin qubits in semiconductors, on-chip long distance entanglement brings versatility to connect quantum core units. Here we realize the controlled and coherent transfer of a pair of entangled electron spins, and demonstrate their remote entanglement when separated by a distance of 6 microns. Driven by coherent spin rotations induced by the electron displacement, high-contrast spin quantum interferences are observed and are a signature of the preservation of the entanglement all along the displacement procedure. This work opens the route towards fast on-chip deterministic interconnection of remote quantum bits in semiconductor quantum circuits., Comment: Main text of 7 pages with 4 figures. Supplementary information of 4 pages with 3 figures

Hole spins in semiconductors are a potential qubit alternative to electron spins. In nuclear-spin-rich host crystals like GaAs, the hyperfine interaction of hole spins with nuclei is considerably weaker than that for electrons, leading to potentially longer dephasing times. Here we demonstrate optical pumping and coherent population trapping for acceptor-bound holes in a strained GaAs epitaxial layer. We find $\ensuremath{\mu}\text{s}$-scale longitudinal spin relaxation time ${T}_{1}$ and an inhomogeneous dephasing time ${T}_{2}^{*}$ of $\ensuremath{\sim}7$ ns. We attribute the spin relaxation mechanism to the combined effect of a hole-phonon interaction through the deformation potentials, and heavy-hole--light-hole mixing in an in-plane magnetic field. We attribute the short ${T}_{2}^{*}$ to $g$-factor broadening due to strain inhomogeneity. ${T}_{1}$ and ${T}_{2}^{*}$ are calculated based on these mechanisms and compared with the experimental results. While the hyperfine-mediated decoherence is mitigated, our results highlight the important contribution of strain to relaxation and dephasing of acceptor-bound hole spins.

The coherent manipulation of individual quantum objects organized in arrays is a prerequisite to any scalable quantum information platform. The cumulated efforts to control electron spins in quantum dot arrays have permitted the recent realization of quantum simulators and multielectron spin-coherent manipulations. Although a natural path to resolve complex quantum-matter problems and to process quantum information, two-dimensional (2D) scaling with a high connectivity of such implementations remains undemonstrated. Here we demonstrate the 2D coherent control of individual electron spins in a 3 × 3 array of tunnel-coupled quantum dots. We focus on several key quantum functionalities: charge-deterministic loading and displacement, local spin readout and local coherent exchange manipulation between two electron spins trapped in adjacent dots. This work lays some of the foundations to exploit a 2D array of electron spins for quantum simulation and information processing. Manipulation of multiple connected quantum objects is mandatory for any scalable quantum information platform. Based on finely tuned virtual gate control, the integration of nearest-neighbour coupled semiconductor quantum dots in a 3 × 3 array enables 2D coherent spin control.

We report on the analysis of electroabsorption in thin GaAs/Al$_{0.3}$Ga$_{0.7}$As nanophotonic waveguides with an embedded $p$-$i$-$n$ junction. By measuring the transmission through waveguides of different lengths, we derive the propagation loss as a function of electric field, wavelength, and temperature. The results are in good agreement with the Franz-Keldysh model of electroabsorption extending over 200 meV below the GaAs bandgap, i.e. in the 910--970 nm wavelength range. We find a pronounced residual absorption in forward bias, which we attribute to Fermi-level pinning at the waveguide surface, producing over 20 dB/mm loss at room temperature. These results are essential for understanding the origin of loss in nanophotonic devices operating in the emission range of self-assembled InAs semiconductor quantum dots, towards the realization of scalable quantum photonic integrated circuits., 6 pages, 3 figures

7 pags., 4 figs., Coherent photon-emitter interfaces offer a way to mediate efficient nonlinear photon-photon interactions, much needed for quantum information processing. Here we experimentally study the case of a two-level emitter, a quantum dot, coupled to a single optical mode in a nanophotonic waveguide. We carry out few-photon transport experiments and record the statistics of the light to reconstruct the scattering matrix elements of one- and two-photon components. This provides direct insight to the complex nonlinear photon interaction that contains rich many-body physics., We gratefully acknowledge financial support from Danmarks Grundforskningsfond (DNRF 139, Hy-Q Center for Hybrid Quantum Networks), H2020 European Research Council (ERC) (SCALE), Styrelsen for Forskning og Innovation (FI) (5072-00016B QUANTECH), Bundesministerium fur Bildung und Forschung (BMBF) (16KIS0867, Q.Link.X), and Deutsche Forschungsgemeinschaft (DFG) (TRR 160). T. R. and J. J. G.-R. acknowledge support from Project No. PGC2018-094792-B-I00 (MCIU/AEI/FEDER, UE), CAM/FEDER Project No. S2018/TCS-4342 (QUITEMAD-CM), and CSIC Quantum Technology Platform PT-001. T. R. further acknowledges funding from the EU Horizon 2020 program under the Marie Skłodowska-Curie Grant Agreement No. 798397

One dimensional semiconductor systems with strong spin-orbit interaction are both of fundamental interest and have potential applications to topological quantum computing. Applying a magnetic field can open a spin gap, a pre-requisite for Majorana zero modes. The spin gap is predicted to manifest as a field dependent dip on the first 1D conductance plateau. However, disorder and interaction effects make identifying spin gap signatures challenging. Here we study experimentally and numerically the 1D channel in a series of low disorder p-type GaAs quantum point contacts, where spin-orbit and hole-hole interactions are strong. We demonstrate an alternative signature for probing spin gaps, which is insensitive to disorder, based on the linear and non-linear response to the orientation of the applied magnetic field, and extract a spin-orbit gap ΔE ≈ 500 μeV. This approach could enable one-dimensional hole systems to be developed as a scalable and reproducible platform for topological quantum applications., In one-dimensional systems, the combination of a strong spin-orbit interaction and an applied magnetic field can give rise to a spin-gap, however experimental identification is difficult. Here, the authors present new signatures for the spin-gap, and verify these experimentally in hole QPCs.