Publications (43)
20 Second Parity Lifetime in an InAs--Pb Tetron Device
Morteza Aghaee, Zulfi Alam, Mariusz Andrzejczuk +162
A central promise of topological quantum computing is that increasing the excitation gap improves device performance significantly. Here, we experimentally validate this principle…
Long-Distance Superexchange between Semiconductor Quantum-Dot Electron Spins
Haifeng Qiao, Yadav P. Kandel, Saeed Fallahi +4
Because of their long coherence times and potential for scalability, semiconductor quantum-dot spin qubits hold great promise for quantum information processing. However, maintaini…
Fast spin exchange between two distant quantum dots
Filip K. Malinowski, Frederico Martins, Thomas B. Smith +8
The Heisenberg exchange interaction between neighboring quantum dots allows precise voltage control over spin dynamics, due to the ability to precisely control the overlap of orbit…
Remote entropy measurement in coupled quantum dots
Owen Sheekey, Tim Child, Elena Cornick +8
Recent experiments have demonstrated that measurements of the entropy change associated with the addition of electrons to semiconductor- and graphene-based quantum dots accurately…
Adiabatic quantum state transfer in a semiconductor quantum-dot spin chain
Yadav P. Kandel, Haifeng Qiao, Saeed Fallahi +3
Semiconductor quantum-dot spin qubits are a promising platform for quantum computation, because they are scalable and possess long coherence times. In order to realize this full po…
Coherent multi-spin exchange coupling in a quantum-dot spin chain
Haifeng Qiao, Yadav P. Kandel, Kuangyin Deng +5
Heisenberg exchange coupling between neighboring electron spins in semiconductor quantum dots provides a powerful tool for quantum information processing and simulation. Although s…
Quantum capacitance anomalies of two-dimensional non-equilibrium states under microwave irradiation
Jian Mi, Jianli Wang, Saeed Fallahi +3
We report our direct study of the compressibility on ultrahigh mobility two-dimensional electron system ( cm/Vs) in GaAs/AlGaAs quantum wells und…
Negative spin exchange in a multielectron quantum dot
Frederico Martins, Filip K. Malinowski, Peter D. Nissen +5
By operating a one-electron quantum dot (fabricated between a multielectron dot and a one-electron reference dot) as a spectroscopic probe, we study the spin properties of a gate-c…
Distinct Lifetimes for and Loop Measurements in a Majorana Tetron Device
Morteza Aghaee, Zulfi Alam, Rikke Andersen +164
We present a hardware realization and measurements of a tetron qubit device in a superconductor-semiconductor heterostructure. The device architecture contains two parallel superco…
Conditional Teleportation of Quantum-Dot Spin States
Haifeng Qiao, Yadav P. Kandel, Sreenath K. Manikandan +5
Among the different platforms for quantum information processing, individual electron spins in semiconductor quantum dots stand out for their long coherence times and potential for…
Entropic signatures of the single-impurity Kondo state
Johann Drayne, Silvia Lüscher, Will Grant +8
The paper reports a thermodynamic measurement of the entropy reduction that occurs when a Kondo singlet forms in a strongly coupled GaAs quantum dot, using temperature‑dependent ch…
Optimization of edge state velocity in the integer quantum Hall regime
Harshad Sahasrabudhe, Bozidar Novakovic, James Nakamura +5
Observation of interference in the quantum Hall regime may be hampered by a small edge state velocity due to finite phase coherence time. Therefore designing two quantum point cont…
Interferometric Single-Shot Parity Measurement in an InAs-Al Hybrid Device
Morteza Aghaee, Alejandro Alcaraz Ramirez, Zulfi Alam +159
The fusion of non-Abelian anyons or topological defects is a fundamental operation in measurement-only topological quantum computation. In topological superconductors, this operati…
Quantum Lifetime in Ultra-High Quality GaAs Quantum Wells: Relationship to and Impact of Density Fluctuations
Qi Qian, James R. Nakamura, Saeed Fallahi +6
We consider quantum lifetime derived from low-field Shubnikov-de Haas oscillations as a metric of quality of the two-dimensional electron gas in GaAs quantum wells that expresses l…
Response to recent comments on Phys. Rev. B 107, 245423 (2023) and Subsection S4.3 of the Supp. Info. for Nature 638, 651-655 (2025)
Morteza Aghaee, Zulfi Alam, Mariusz Andrzejczuk +127
The topological gap protocol (TGP) is a statistical test designed to identify a topological phase with high confidence and without human bias. It is used to determine a promising p…
Readout Of Singlet-Triplet Qubits At Large Magnetic Field Gradients
Lucas A. Orona, John M. Nichol, Shannon P. Harvey +5
Visibility of singlet-triplet qubit readout is reduced to almost zero in large magnetic field gradients due to relaxation processes. Here we present a new readout technique that is…
High temperature resistivity measured at ν = 5/2 as a predictor of 2DEG quality in the N=1 Landau level
Qi Qian, James R. Nakamura, Saeed Fallahi +3
We report a high temperature (T = 0.3K) indicator of the excitation gap at the filling factor fractional quantum Hall state in ultra-high quality AlGaAs/GaAs t…
Field-effect-induced two-dimensional electron gas utilizing modulation doping for improved ohmic contacts
Sumit Mondal, Geoffrey C. Gardner, John D. Watson +3
Modulation-doped AlGaAs/GaAs heterostructures are utilized extensively in the study of quantum transport in nanostructures, but charge fluctuations associated with remote ionized d…
Anderson Orthogonality as Measurement Backaction in Coupled Quantum Dots
Will Grant, Sarath Sankar, Elena Cornick +9
Measurement perturbs a quantum system by coupling it to external degrees of freedom, but detector backaction depends on the physical mechanism of measurement itself. In solid-state…
Observation of new plasmons in the fractional quantum Hall effect: interplay of topological and nematic orders
Lingjie Du, Ursula Wurstbauer, Ken W. West +5
Collective modes of exotic quantum fluids reveal underlying physical mechanisms responsible for emergent complex quantum ground states. We observe unexpected new collective modes i…
Coherent spin state transfer via Heisenberg exchange
Yadav P. Kandel, Haifeng Qiao, Saeed Fallahi +3
Quantum information science has the potential to revolutionize modern technology by providing resource-efficient approaches to computing, communication, and sensing. Although the p…
Noise suppression using symmetric exchange gates in spin qubits
Frederico Martins, Filip K. Malinowski, Peter D. Nissen +6
We demonstrate a substantial improvement in the spin-exchange gate using symmetric control instead of conventional detuning in GaAs spin qubits, up to a factor-of-six increase in t…
Modified MBE hardware and techniques and role of gallium purity for attainment of two dimensional electron gas mobility >35 x10^6 cm^2/Vs in AlGaAs/GaAs quantum wells grown by MBE
Geoffrey C. Gardner, Saeed Fallahi, John D. Watson +1
We provide evidence that gallium purity is the primary impediment to attainment of ultra-high mobility in a two-dimensional electron gas (2DEG) in AlGaAs/GaAs heterostructures grow…
Spectrum of the Nuclear Environment for GaAs Spin Qubits
Filip K. Malinowski, Frederico Martins, Åukasz CywiÅski +7
Using a singlet-triplet spin qubit as a sensitive spectrometer of the GaAs nuclear spin bath, we demonstrate that the spectrum of Overhauser noise agrees with a classical spin diff…
Shubnikov-de Haas Characterization of Superconductor-Semiconductor Heterostructures
A. M. Zimmerman, Saeed Fallahi, Sergei Gronin +13
Hybrid superconductor-semiconductor nanostructures are a central component for research spanning condensed matter physics and quantum information processing. Continued progress rel…
InAs-Al Hybrid Devices Passing the Topological Gap Protocol
Morteza Aghaee, Arun Akkala, Zulfi Alam +124
We present measurements and simulations of semiconductor-superconductor heterostructure devices that are consistent with the observation of topological superconductivity and Majora…
Aharonov-Bohm interference of fractional quantum Hall edge modes
James Nakamura, Saeed Fallahi, Harshad Sahasrabudhe +4
We demonstrate operation of a small Fabry-Perot interferometer in which highly coherent Aharonov-Bohm oscillations are observed in the integer and fractional quantum Hall regimes.…
Physics-informed tracking of qubit fluctuations
Fabrizio Berritta, Jan A. Krzywda, Jacob Benestad +9
Environmental fluctuations degrade the performance of solid-state qubits but can in principle be mitigated by real-time Hamiltonian estimation down to time scales set by the estima…
Precision measurement of electron-electron scattering in GaAs/AlGaAs using transverse magnetic focusing
Adbhut Gupta, Jean J. Heremans, Gitansh Kataria +4
Electron-electron (e-e) interactions assume a cardinal role in solid-state physics. Quantifying the e-e scattering length is hence critical. In this paper we show that the mesoscop…
Observation of flat bands in gated semiconductor artificial graphene
Lingjie Du, Ziyu Liu, Shalom J. Wind +6
Flat bands near M points in the Brillouin zone are key features of honeycomb symmetry in artificial graphene (AG) where electrons may condense into novel correlated phases. Here we…
Roadmap to fault tolerant quantum computation using topological qubit arrays
David Aasen, Morteza Aghaee, Zulfi Alam +179
We describe a concrete device roadmap towards a fault-tolerant quantum computing architecture based on noise-resilient, topologically protected Majorana-based qubits. Our roadmap e…
Spin of a multielectron quantum dot and its interaction with a neighboring electron
Filip K. Malinowski, Frederico Martins, Thomas B. Smith +8
We investigate the spin of a multielectron GaAs quantum dot in a sequence of nine charge occupancies, by exchange coupling the multielectron dot to a neighboring two-electron doubl…
Simultaneous Operations in a Two-Dimensional Array of Singlet-Triplet Qubits
Federico Fedele, Anasua Chatterjee, Saeed Fallahi +3
In many physical approaches to quantum computation, error-correction schemes assume the ability to form two-dimensional qubit arrays with nearest-neighbor couplings and parallel op…
Fractional focusing peaks and collective dynamics in two-dimensional Fermi liquids
Adbhut Gupta, Gitansh Kataria, Mani Chandra +6
Carrier transport in materials is often diffusive due to momentum-relaxing scattering with phonons and defects. Suppression of momentum-relaxing scattering can lead to the ballisti…
Real-time two-axis control of a spin qubit
Fabrizio Berritta, Torbjørn Rasmussen, Jan A. Krzywda +9
Optimal control of qubits requires the ability to adapt continuously to their ever-changing environment. We demonstrate a real-time control protocol for a two-electron singlet-trip…
Magnetically-defined topological edge plasmons in edgeless electron gas
Dafei Jin, Yang Xia, Thomas Christensen +11
Topological materials bear gapped excitations in bulk yet protected gapless excitations at boundaries. Magnetoplasmons (MPs), as high-frequency density excitations of two-dimension…
Direct Entropy Measurement in a Mesoscopic Quantum System
Nikolaus Hartman, Christian Olsen, Silvia Lüscher +5
The entropy of an electronic system offers important insights into the nature of its quantum mechanical ground state. This is particularly valuable in cases where the state is diff…
Entropy measurement of a strongly coupled quantum dot
Tim Child, Owen Sheekey, Silvia Lüscher +8
The spin 1/2 entropy of electrons trapped in a quantum dot has previously been measured with great accuracy, but the protocol used for that measurement is valid only within a restr…
Floquet-Enhanced Spin Swaps
Haifeng Qiao, Yadav P. Kandel, John S. Van Dyke +5
The transfer of information between quantum systems is essential for quantum communication and computation. In quantum computers, high connectivity between qubits can improve the e…
Automated in situ optimization and disorder mitigation in a quantum device
Jacob Benestad, Torbjørn Rasmussen, Bertram Brovang +9
We investigate automated in situ optimization of the potential landscape in a quantum point contact device, using a gate array patterned atop the constriction. Optimiz…
Symmetric Operation of the Resonant Exchange Qubit
Filip K. Malinowski, Frederico Martins, Peter D. Nissen +5
We operate a resonant exchange qubit in a highly symmetric triple-dot configuration using IQ-modulated RF pulses. At the resulting three-dimensional sweet spot the qubit splitting…
A robust protocol for entropy measurement in mesoscopic circuits
Tim Child, Owen Sheekey, Silvia Lüscher +4
Previous measurements utilizing Maxwell relations to measure change in entropy, , demonstrated remarkable accuracy of measuring the spin-1/2 entropy of electrons in a weakly cou…
High-fidelity entangling gate for double-quantum-dot spin qubits
John M. Nichol, Lucas A. Orona, Shannon P. Harvey +4
Electron spins in semiconductors are promising qubits because their long coherence times enable nearly 10^9 coherent quantum gate operations. However, developing a scalable high-fi…