Improved Single Shot Quantum Measurement using Superconducting Circuits

Abstract

Harnessing the properties of quantum systems – parallelism and quantum interference have enabled us to demonstrate quantum supremacy over classical computers. Using the circuit model and quantum information processing is realized on natural microscopic quantum systems such as quantum dots, trapped ions, ultracold atoms, NV centers in diamonds. However superconducting circuits, being macroscopic have controllable parameters and scalable prospects and are ideal candidates for qubits . The coupled system of the circuit and the cavity, probed at microwave frequencies can be realized as an atom in a cavity (as in cavityQED) whose Hamiltonian resembles a two-level system(atom/circuit) coupled to a harmonic oscillator -the Jaynes Cummings Hamiltonian .Various circuit designs an control techniques has resulted in various types of qubits – flux, charge and phase qubits and hybrids ( fluxonium , Xmon . . . ) .The transmon qubit, due to reduced charge noise is most prominent qubit design . Multiple qubit architectures with tunable resonator couplings are designed and various quantum algorithms have been implemented to demonstrate exponential advantage over classical counterparts. Implementing multi-qubit algorithms require single-shot measurement of each qubit after applying coherent gates. Moreover state tomography, quantum teleportation, and quantum cryptography requires high-fidelity single shot measurements. Improving upon it, real time high-fidelity readout with further reduced measurement back-action was achieved with measurement-based feedback controllers. Commercial field-programmable gate array (FPGA) systems, can stabilize single-shot measurements by reducing the feedback measurement noise on the qubit, and reading out the qubit state simultaneously in real time. FPGA controller systems have been used to reset a single qubit to the ground state and to stabilize entangled states. We propose to implement a similar measurement-based feedback scheme using high speed controllers (FPGAs) to stabilize qubits after single-shot measurements. Dispersive readout signals would be amplified via Josephson parametric amplification process before feeding into the feedback controller sensors. Using such a setup, we wish to stabilize multiple-qubit single-shot measurements up to high fidelities. We also aim to study the long-term fluctuations of qubits and calculate the spectral noise at higher frequencies by increasing repeated measurement as well as study correlation between qubit decoherence and readout frequencies using the FPGA setup.