On-demand generation and characterization of a microwave time-bin qubit

Abstract

Superconducting circuits offer a scalable platform for the construction of large-scale quantum networks where information can be encoded in multiple temporal modes of propagating microwaves. Characterization of such microwave signals with a method extendable to an arbitrary number of temporal modes with a single detector and demonstration of their phase-robust nature are of great interest. Here we show the on-demand generation and Wigner tomography of a microwave timebin qubit with superconducting circuit quantum electrodynamics architecture. We perform the tomography with a single heterodyne detector by dynamically changing the measurement quadrature with a phase-sensitive amplifier independently for the two temporal modes. By generating and measuring the qubits with hardware lacking a shared phase reference, we demonstrate conservation of phase information in each time-bin qubit generated.

Realizing a deterministic source of multipartite-entangled photonic qubits

“…3 and Supplementary Note 4 for a detailed discussion of the tomography method). Reconstructing the joint density matrix of four modes is well beyond what has been demonstrated previously for propagating microwave fields, which is full tomography for up to two modes 22 – 24 . We note that full tomography for even more than four modes is possible by further extending the capacity of data storage on the FPGA or by using offline data processing solutions.…”

Fast readout and reset of a superconducting qubit coupled to a resonator with an intrinsic Purcell filter

“…It is also important to quickly reset the leakage error in the second excited state of the qubits, which can build up and significantly degrade the errorcorrecting performance [29,30]. The low-Q resonator and the efficient off-resonant driving are also useful for rapidly generating and absorbing itinerant microwave photons, which can mediate inter-node communication in a quantum network [31][32][33][34][35].…”

Remote Entanglement of Superconducting Qubits via Solid-State Spin Quantum Memories

“…A difference between these two protocols is whether the superconducting qubit or the spin is the emitter (receiver) of the microwave time-bin qubit. Efficient (> 90%) microwave time-bin qubit generation and absorption by the superconducting qubit have been demonstrated [27,35], suggesting that the superconducting qubit can be used in both ways with similar efficiency. Thus, the efficiency of microwave emission or absorption by the color center spins determines which protocols to choose.…”

“…On the basis of both schemes, we estimate an actual entanglement generation rate between the superconducting qubit and the spin. For a superconducting qubit coupled to a cavity, the generation or absorption of a microwave time-bin qubit takes several hundreds of nanoseconds to a few microseconds [27,35]. Here, we assume that it takes 1 µs to generate or absorb a microwave time-bin Fig.…”

“…where r sc-sc is the entanglement attempt rate corresponding to the speed with which the microwave time-bin qubit is generated at a superconducting qubit, η DC is the microwave-to-optical conversion efficiency, and η DC loss includes all losses during the propagation of the photon. For the calculation of R DC sc-sc , we assumed that the superconducting qubit coupled to the microwave cavity can generate a microwave time-bin qubit at a rate of r sc-sc =1 MHz [27,35]. Here, for simplicity, we do not consider the detail of the transducer.…”