Seit seiner ersten Entdeckung hat der Quanten-Hall-Effekt aufgrund seiner faszinierenden Physik u... more Seit seiner ersten Entdeckung hat der Quanten-Hall-Effekt aufgrund seiner faszinierenden Physik und seiner potenziellen realen Anwendungen die Aufmerksamkeit vieler Forscher auf sich gezogen. Tatsächlich weisen Materialien im Quanten-Hall-Regime bemerkenswerte physikalische Eigenschaften auf, die sich in verschiedenen Zweigen der angewandten Wissenschaft als nützlich erweisen können. In dieser Arbeit suchen wir nach Möglichkeiten, diese Materialien im Kontext der Quantenberechnung einzusetzen. Quanten-Hall-Systeme sind im Inneren isolierend, weisen jedoch an den Rändern lückenlose Zustände auf, die dissipationsfreie leitende Kanäle liefern. Aus diesem Grund ist die Antwort auf von außen angelegte elektrische Felder mit energiearmen Anregungen verbunden, die an den Rändern der Probe lokalisiert sind. Wir präsentieren ein Modell zur Beschreibung der Dynamik dieser Anregungen und spezialisieren uns auf Systeme, bei denen das Quanten-Hall-Material kapazitiv an externe Elektroden gekoppe...
Hole spin qubits in quasi one-dimensional structures are a promising platform for quantum informa... more Hole spin qubits in quasi one-dimensional structures are a promising platform for quantum information processing because of the strong spin-orbit interaction (SOI). We present analytical results and discuss device designs that optimize the SOI in Ge semiconductors. We show that at the magnetic field values at which qubits are operated, orbital effects of magnetic fields can strongly affect the response of the spin qubit. We study one-dimensional hole systems in Ge under the influence of electric and magnetic fields applied perpendicularly to the device. In our theoretical description, we include these effects exactly. The orbital effects lead to a strong renormalization of the g-factor. We find a sweet-spot of the nanowire (NW) g-factor where charge noise is strongly suppressed and present an effective low-energy model that captures the dependence of the SOI on the electromagnetic fields. Moreover, we compare properties of NWs with square and circular cross-sections with ones of gat...
Hole spin qubits in planar Ge heterostructures are one of the frontrunner platforms for scalable ... more Hole spin qubits in planar Ge heterostructures are one of the frontrunner platforms for scalable quantum computers. In these systems, the spin-orbit interactions permit efficient all-electric qubit control. We propose a minimal design modification of planar devices that enhances these interactions by orders of magnitude and enables low power ultrafast qubit operations in the GHz range. Our approach is based on an asymmetric potential that strongly squeezes the quantum dot in one direction. This confinement-induced spin-orbit interaction does not rely on microscopic details of the device such as growth direction or strain, and could be turned on and off on demand in state-of-the-art qubits.
The strong spin-orbit coupling in hole spin qubits enables fast and electrically tunable gates, b... more The strong spin-orbit coupling in hole spin qubits enables fast and electrically tunable gates, but at the same time enhances the susceptibility of the qubit to charge noise. Suppressing this noise is a significant challenge in semiconductor quantum computing. Here, we show theoretically that hole Si fin field-effect transistors (FinFETs) are not only very compatible with modern CMOS technology, but they present operational sweet spots where the charge noise is completely removed. The presence of these sweet spots is a result of the interplay between the anisotropy of the material and the triangular shape of the FinFET cross section, and it does not require an extreme fine-tuning of the electrostatics of the device. We present how the sweet spots appear in FinFETs grown along different crystallographic axes and we study in detail how the behavior of these devices changes when the cross-section area and aspect ratio are varied. We identify designs that maximize the qubit performance and could pave the way towards a scalable spin-based quantum computer.
We present a circuit design composed of a non-reciprocal device and Josephson junctions whose gro... more We present a circuit design composed of a non-reciprocal device and Josephson junctions whose ground space is doubly degenerate and the ground states are approximate codewords of the Gottesman-Kitaev-Preskill (GKP) code. We determine the low-energy dynamics of the circuit by working out the equivalence of this system to the problem of a single electron confined in a twodimensional plane and under the effect of strong magnetic field and of a periodic potential. We find that the circuit is naturally protected against the common noise channels in superconducting circuits, such as charge and flux noise, implying that it can be used for passive quantum error correction. We also propose realistic design parameters for an experimental realization and we describe possible protocols to perform logical one-and two-qubit gates, state preparation and readout.
We theoretically investigate the simulation of moving cavities in a superconducting circuit setup... more We theoretically investigate the simulation of moving cavities in a superconducting circuit setup. In particular, we consider a recently proposed experimental scenario where the phase of the cavity field is used as a moving clock. By computing the error made when simulating the cavity trajectory with SQUIDs, we identify parameter regimes where the correspondence holds, and where time dilation, as well as corrections due to clock size and particle creation coefficients, are observable. These findings may serve as a guideline when performing experiments on simulation of moving cavities in superconducting circuits.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and instit... more Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Stimulated by the recent implementation of a three-port Hall-effect microwave circulator of Mahon... more Stimulated by the recent implementation of a three-port Hall-effect microwave circulator of Mahoney et al. (MEA), we present model studies of the performance of this device. Our calculations are based on the capacitive-coupling model of Viola and DiVincenzo (VD). Based on conductance data from a typical Hall-bar device obtained from a two-dimensional electron gas (2DEG) in a magnetic field, we numerically solve the coupled field-circuit equations to calculate the expected performance of the circulator, as determined by the S parameters of the device when coupled to 50 ports, as a function of frequency and magnetic field. Above magnetic fields of 1.5 T, for which a typical 2DEG enters the quantum Hall regime (corresponding to a Landau-level filling fraction ν of 20), the Hall angle θ H = tan-1 σ xy /σ xx always remains close to 90°, and the S parameters are close to the analytic predictions of VD for θ H = π/2. As anticipated by VD, MEA find the device to have rather high (k) impedance, and thus to be extremely mismatched to 50 , requiring the use of impedance matching. We incorporate the lumped matching circuits of MEA in our modeling and confirm that they can produce excellent circulation, although confined to a very small bandwidth. We predict that this bandwidth is significantly improved by working at lower magnetic field when the Landau index is high, e.g. ν = 20, and the impedance mismatch is correspondingly less extreme. Our modeling also confirms the observation of MEA that parasitic port-to-port capacitance can produce very interesting countercirculation effects.
Hole spin qubits are frontrunner platforms for scalable quantum computers, but state-of-theart de... more Hole spin qubits are frontrunner platforms for scalable quantum computers, but state-of-theart devices suffer from noise originating from the hyperfine interactions with nuclear defects. We show that these interactions have a highly tunable anisotropy that is controlled by device design and external electric fields. This tunability enables sweet spots where the hyperfine noise is suppressed by an order of magnitude and is comparable to isotopically purified materials. We identify surprisingly simple designs where the qubits are highly coherent and are largely unaffected by both charge and hyperfine noise. We find that the large spin-orbit interaction typical of elongated quantum dots not only speeds up qubit operations, but also dramatically renormalizes the hyperfine noise, altering qualitatively the dynamics of driven qubits and enhancing the fidelity of qubit gates. Our findings serve as guidelines to design high performance qubits for scaling up quantum computers.
Seit seiner ersten Entdeckung hat der Quanten-Hall-Effekt aufgrund seiner faszinierenden Physik u... more Seit seiner ersten Entdeckung hat der Quanten-Hall-Effekt aufgrund seiner faszinierenden Physik und seiner potenziellen realen Anwendungen die Aufmerksamkeit vieler Forscher auf sich gezogen. Tatsächlich weisen Materialien im Quanten-Hall-Regime bemerkenswerte physikalische Eigenschaften auf, die sich in verschiedenen Zweigen der angewandten Wissenschaft als nützlich erweisen können. In dieser Arbeit suchen wir nach Möglichkeiten, diese Materialien im Kontext der Quantenberechnung einzusetzen. Quanten-Hall-Systeme sind im Inneren isolierend, weisen jedoch an den Rändern lückenlose Zustände auf, die dissipationsfreie leitende Kanäle liefern. Aus diesem Grund ist die Antwort auf von außen angelegte elektrische Felder mit energiearmen Anregungen verbunden, die an den Rändern der Probe lokalisiert sind. Wir präsentieren ein Modell zur Beschreibung der Dynamik dieser Anregungen und spezialisieren uns auf Systeme, bei denen das Quanten-Hall-Material kapazitiv an externe Elektroden gekoppe...
Hole spin qubits in quasi one-dimensional structures are a promising platform for quantum informa... more Hole spin qubits in quasi one-dimensional structures are a promising platform for quantum information processing because of the strong spin-orbit interaction (SOI). We present analytical results and discuss device designs that optimize the SOI in Ge semiconductors. We show that at the magnetic field values at which qubits are operated, orbital effects of magnetic fields can strongly affect the response of the spin qubit. We study one-dimensional hole systems in Ge under the influence of electric and magnetic fields applied perpendicularly to the device. In our theoretical description, we include these effects exactly. The orbital effects lead to a strong renormalization of the g-factor. We find a sweet-spot of the nanowire (NW) g-factor where charge noise is strongly suppressed and present an effective low-energy model that captures the dependence of the SOI on the electromagnetic fields. Moreover, we compare properties of NWs with square and circular cross-sections with ones of gat...
Hole spin qubits in planar Ge heterostructures are one of the frontrunner platforms for scalable ... more Hole spin qubits in planar Ge heterostructures are one of the frontrunner platforms for scalable quantum computers. In these systems, the spin-orbit interactions permit efficient all-electric qubit control. We propose a minimal design modification of planar devices that enhances these interactions by orders of magnitude and enables low power ultrafast qubit operations in the GHz range. Our approach is based on an asymmetric potential that strongly squeezes the quantum dot in one direction. This confinement-induced spin-orbit interaction does not rely on microscopic details of the device such as growth direction or strain, and could be turned on and off on demand in state-of-the-art qubits.
The strong spin-orbit coupling in hole spin qubits enables fast and electrically tunable gates, b... more The strong spin-orbit coupling in hole spin qubits enables fast and electrically tunable gates, but at the same time enhances the susceptibility of the qubit to charge noise. Suppressing this noise is a significant challenge in semiconductor quantum computing. Here, we show theoretically that hole Si fin field-effect transistors (FinFETs) are not only very compatible with modern CMOS technology, but they present operational sweet spots where the charge noise is completely removed. The presence of these sweet spots is a result of the interplay between the anisotropy of the material and the triangular shape of the FinFET cross section, and it does not require an extreme fine-tuning of the electrostatics of the device. We present how the sweet spots appear in FinFETs grown along different crystallographic axes and we study in detail how the behavior of these devices changes when the cross-section area and aspect ratio are varied. We identify designs that maximize the qubit performance and could pave the way towards a scalable spin-based quantum computer.
We present a circuit design composed of a non-reciprocal device and Josephson junctions whose gro... more We present a circuit design composed of a non-reciprocal device and Josephson junctions whose ground space is doubly degenerate and the ground states are approximate codewords of the Gottesman-Kitaev-Preskill (GKP) code. We determine the low-energy dynamics of the circuit by working out the equivalence of this system to the problem of a single electron confined in a twodimensional plane and under the effect of strong magnetic field and of a periodic potential. We find that the circuit is naturally protected against the common noise channels in superconducting circuits, such as charge and flux noise, implying that it can be used for passive quantum error correction. We also propose realistic design parameters for an experimental realization and we describe possible protocols to perform logical one-and two-qubit gates, state preparation and readout.
We theoretically investigate the simulation of moving cavities in a superconducting circuit setup... more We theoretically investigate the simulation of moving cavities in a superconducting circuit setup. In particular, we consider a recently proposed experimental scenario where the phase of the cavity field is used as a moving clock. By computing the error made when simulating the cavity trajectory with SQUIDs, we identify parameter regimes where the correspondence holds, and where time dilation, as well as corrections due to clock size and particle creation coefficients, are observable. These findings may serve as a guideline when performing experiments on simulation of moving cavities in superconducting circuits.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and instit... more Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Stimulated by the recent implementation of a three-port Hall-effect microwave circulator of Mahon... more Stimulated by the recent implementation of a three-port Hall-effect microwave circulator of Mahoney et al. (MEA), we present model studies of the performance of this device. Our calculations are based on the capacitive-coupling model of Viola and DiVincenzo (VD). Based on conductance data from a typical Hall-bar device obtained from a two-dimensional electron gas (2DEG) in a magnetic field, we numerically solve the coupled field-circuit equations to calculate the expected performance of the circulator, as determined by the S parameters of the device when coupled to 50 ports, as a function of frequency and magnetic field. Above magnetic fields of 1.5 T, for which a typical 2DEG enters the quantum Hall regime (corresponding to a Landau-level filling fraction ν of 20), the Hall angle θ H = tan-1 σ xy /σ xx always remains close to 90°, and the S parameters are close to the analytic predictions of VD for θ H = π/2. As anticipated by VD, MEA find the device to have rather high (k) impedance, and thus to be extremely mismatched to 50 , requiring the use of impedance matching. We incorporate the lumped matching circuits of MEA in our modeling and confirm that they can produce excellent circulation, although confined to a very small bandwidth. We predict that this bandwidth is significantly improved by working at lower magnetic field when the Landau index is high, e.g. ν = 20, and the impedance mismatch is correspondingly less extreme. Our modeling also confirms the observation of MEA that parasitic port-to-port capacitance can produce very interesting countercirculation effects.
Hole spin qubits are frontrunner platforms for scalable quantum computers, but state-of-theart de... more Hole spin qubits are frontrunner platforms for scalable quantum computers, but state-of-theart devices suffer from noise originating from the hyperfine interactions with nuclear defects. We show that these interactions have a highly tunable anisotropy that is controlled by device design and external electric fields. This tunability enables sweet spots where the hyperfine noise is suppressed by an order of magnitude and is comparable to isotopically purified materials. We identify surprisingly simple designs where the qubits are highly coherent and are largely unaffected by both charge and hyperfine noise. We find that the large spin-orbit interaction typical of elongated quantum dots not only speeds up qubit operations, but also dramatically renormalizes the hyperfine noise, altering qualitatively the dynamics of driven qubits and enhancing the fidelity of qubit gates. Our findings serve as guidelines to design high performance qubits for scaling up quantum computers.
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