Quantum control of an oscillator using a stimulated Josephson nonlinearity

Abstract

Superconducting circuits extensively rely on the Josephson junction as a nonlinear electronic element for manipulating quantum information and mediating photon interactions. Despite continuing efforts in designing anharmonic Josephson circuits with improved coherence times, the best photon lifetimes have been demonstrated in microwave cavities. Nevertheless, architectures based on quantum memories need a qubit element for addressing these harmonic modules at the cost of introducing additional loss channels and limiting process fidelities. This work focuses on tailoring the oscillator Hilbert space to enable a direct Rabi drive on individual energy levels. For this purpose we implement a flux-tunable inductive coupling between two linear resonators using a superconducting quantum interference device. We dynamically activate a three-wave mixing process through parametric flux modulation in order to selectively address the lowest eigenstates as an isolated two-level system. Measuring the Wigner function confirms we can prepare arbitrary states confined in the single photon manifold, with measured coherence times limited by the oscillator intrinsic quality factor. This architectural shift in engineering oscillators with stimulated nonlinearity can be exploited for designing long-lived quantum modules and offers flexibility in studying non-equilibrium physics with photons in a field-programmable simulator.Quantized electromagnetic excitations in superconducting circuits have become a promising platform for processing quantum information 1 . A central piece to this hardware is the Josephson effect, which grants nonlinearity with negligible dissipation. Nonlinear mesoscopic oscillators have been attracting much interest in studying non-equilibrium physics 2 . Electrical circuits composed of Josephson junctions behave as quantum systems with discrete energy levels resembling artificial atoms 3 . Although the coherence properties of anharmonic Josephson circuits have been improving these past two decades, storing microwave photons in harmonic oscillators leads to significantly longer coherence times 4,5 . This promising development has launched efforts in building hardwareefficient architectures based on quantum memories 6,7 . Since it is impossible to selectively address individual transitions in a harmonic system, Josephson qubits are used for preparing and transferring quantum information with negative impact on coherence and gate fidelities. In this work we present a new paradigm in exploiting the Josephson effect to perform logical operations directly on the oscillator Hilbert space using a dynamically activated nonlinearity.The key concept behind this experiment is to engineer a three-wave interaction between the electromagnetic modes of two linear oscillators, which we refer to as logical and blockade oscillator (Fig. 1A). Parametrically modulating the interaction amplitude stimulates the conversion of two logical photons into one blockade photon and vice-versa. Provided the conversion rate is larger than the oscil...

A Quantum System Control Method Based on Enhanced Reinforcement Learning

“…It should be noted that our method is sufficient for the evolution of quantum state in spin 1/2 system. Other difficult quantum control problems include quantum error correction based on bosonic codes (Michael et al 2016) and quantum state preparation in the singlephoton manifold (Vrajitoarea et al 2020). And it is a valuable work to conduct a study on providing solu-tions by using learning theories (Li et al 2018;Zhang and Wang 2020) and neural network (Xu et al 2019;Hu et al 2020), which is also one of our next research.…”

Observation of magnon cross-Kerr effect in cavity magnonics

“…Nonlinearity and nonlinear interactions are weak and difficult to be detected in some systems, but they can also become sufficiently strong to be the dominant factor in some other systems. The cross-Kerr effect is one of the subtle nonlinear interactions between fields and waves that can exist in natural ions [13], atoms [14][15][16], and artificial mesoscopic architectures, such as superconducting circuits [17][18][19]. The cross-Kerr effect is a nonlinear shift in the frequency of a resonator as a function of the number of excitations in another mode that interacts with the resonator.…”

Direct evidence of microstructure dependence of magnetic flux trapping in niobium

“…However, the achievement of both high Q 0 and high E acc in the same cavity has remained elusive. Beyond SRF accelerator technology, high Q 0 SRF quality Nb is beginning to find application in quantum computing devices 3 , 4 , with the possibility that high Q at very low microwave power at a single photon level may provide a viable approach to increase qubit lifetime 5 , 6 . Hence, understanding the factors that determine Q 0 in SRF Nb is of great interest.…”