Publications

2021

1. arXiv preprint

   Dynamical sweet spot engineering via two-tone flux modulation of superconducting qubits

   J. A Valery, S. Chowdhury, G. Jones, and N. Didier

   arXiv 2104.07835 (submitted to PRX Quantum)

   Abstract arXiv

   Current superconducting quantum processors require strategies for coping with material defects and imperfect parameter targeting in order to scale up while maintaining high performance. To that end, in-situ control of qubit frequencies with magnetic flux can be used to avoid spurious resonances. However, increased dephasing due to 1/f flux noise limits performance at all of these operating points except for noise-protected sweet spots, which are sparse under DC flux bias and monochromatic flux modulation. Here we experimentally demonstrate that two-tone flux modulation can be used to create a continuum of dynamical sweet spots, greatly expanding the range of qubit frequencies achievable while first-order insensitive to slow flux noise. To illustrate some advantages of this flexibility, we use bichromatic flux control to reduce the error rates and gate times of parametric entangling operations between transmons. Independent of gate scheme, the ability to use flux control to freely select qubit frequencies while maintaining qubit coherence represents an important step forward in the robustness and scalability of near-term superconducting qubit devices.

2. In prep.

   Onset of multi-stability for non-linear resonances of a driven oscillator: classical versus quantum regimes

   J. Venkatraman, X. Xiao, Y. Zhang, S. Chowdhury, and M. H. Devoret
3. In prep.

   Engineering arbitrary two-mode Gaussian control interactions in a hybrid multimode device

   S. Chowdhury, M. Zhang, and L. Jiang

2020

1. arXiv preprint

   Interference-based universal decoupling and swapping for multimode bosonic systems

   M. Zhang, S. Chowdhury, and L. Jiang

   arXiv 2007.02385

   Abstract arXiv

   Beam-splitter operations are widely used to process information encoded in bosonic modes. In hybrid quantum systems, however, it might be challenging to implement a reliable beam-splitter operation between two distinct bosonic modes. Without beam-splitters, some basic operations such as decoupling modes and swapping states between modes can become highly non-trivial or not feasible at all. In this work, we develop novel interference-based protocols for decoupling and swapping selected modes of a multimode bosonic system without requiring beam-splitters. Specifically, for a given generic coupler characterized by a Gaussian unitary process, we show how to decouple a single mode or swap any pair of modes with a constant depth sequence of operations, while maintaining the coupling for the remaining system. These protocols require only multiple uses of the given coupler, interleaved with single-mode Gaussian unitary operations, and thus enable efficient construction of operations crucial to quantum information science, such as high-fidelity quantum transduction. Our results are directly derived from fundamental physical properties of bosonic systems and are therefore broadly applicable to various existing platforms.

2017

1. arXiv preprint

   Comparing weak and projective measurements for quantum state tomography of a single-qubit system

   S. Chowdhury

   arXiv 1711.03645

   Abstract arXiv

   We explore the use of weak quantum measurements for single-qubit quantum state tomography processes. Weak measurements are those where the coupling between the qubit and the measurement apparatus is weak; this results in the quantum state being disturbed less than in the case of a projective measurement. We employ a weak measurement tomography protocol developed by Das and Arvind, which they claim offers a new method of extracting information from quantum systems. We test the Das-Arvind scheme for various measurement strengths, and ensemble sizes, and reproduce their results using a sequential stochastic simulation. Lastly, we place these results in the context of current understanding of weak and projective measurements.