Readout of a quantum state in an array of quantum dots

Tzu-Kan Hsiao, Cornelis Jacobus van Diepen, U. Mukhopadhyay +3 more

Günter Mahler A, Rainer Wawer

Pierre Hamonic, Martin Nurizzo, Jayshankar Nath +15 more

Semiconductor quantum dot arrays are a promising platform to perform spin-based error-corrected quantum computation with large numbers of qubits. However, due to the diverging number of possible charge configurations combined with the limited sensitivity of large-footprint charge sensors, achieving single-spin occupancy in each dot in a growing quantum dot array is exceedingly complex. Therefore, to scale-up a spin-based architecture we must change how individual charges are readout and controlled. Here, we demonstrate single-spin occupancy of each dot in a foundry-fabricated array by combining two methods. 1/ Loading a finite number of electrons into the quantum dot array; simplifying electrostatic tuning by isolating the array from the reservoirs. 2/ Deploying multiplex gate-based reflectometry to dispersively probe charge tunneling and spin states without charge sensors or reservoirs. Our isolated arrays probed by embedded multiplex readout can be readily electrostatically tuned. They are thus a viable, scalable approach for spin-based quantum architectures. Large-footprint, low-sensitivity charge sensors hinder scaling semiconductor quantum dot arrays for quantum computation. Here the authors present a potentially scalable approach using multiplexed gate-based readout and operation in a foundry-fabricated quantum dot array, demonstrating single-electron occupancy.

James Colless, Alice Mahoney, J. M. Hornibrook +4 more

We report the dispersive charge-state readout of a double quantum dot in the few-electron regime using the in situ gate electrodes as sensitive detectors. We benchmark this gate sensing technique against the well established quantum point contact charge detector and find comparable performance with a bandwidth of $\ensuremath{\sim}10\text{ }\text{ }\mathrm{MHz}$ and an equivalent charge sensitivity of $\ensuremath{\sim}6.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\text{ }\text{ }e/\sqrt{\mathrm{Hz}}$. Dispersive gate sensing alleviates the burden of separate charge detectors for quantum dot systems and promises to enable readout of qubits in scaled-up arrays.

Neil M. Zimmerman

Martin Nurizzo, Baptiste Jadot, Pierre-André Mortemousque +8 more

Recent demonstrations using electron spins stored in quantum dot 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 dot 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 development to isolate a subpart of the array in a metastable configuration while performing charge displacement and readout in the rest of the system. The degree of control over tunnel coupling achieved in a unit cell should motivate future protocol development for tuning, manipulation, and readout including this capability.