Coherent-state storage and retrieval between superconducting cavities using parametric frequency conversion

Abstract

In superconducting quantum information, machined aluminum superconducting cavities have proven to be a well-controlled, low-dissipation electromagnetic environment for quantum circuits such as qubits. They can possess large internal quality factors, Q int > 10 8 , and present the possibility of storing quantum information for times far exceeding those of microfabricated circuits. However, in order to be useful as a storage element, these cavities require a fast "read/write" mechanism-in other words, they require tunable coupling between other systems of interest such as other cavity modes and qubits, as well as any associated readout hardware. In this work, we demonstrate these qualities in a simple dual cavity architecture in which a low-Q "readout" mode is parametrically coupled to a high-Q "storage" mode, allowing us to store and retrieve classical information. Specifically, we employ a flux-driven Josephson junction-based coupling scheme to controllably swap coherent states between two cavities, demonstrating full, sequenced control over the coupling rates between modes.Quantum optics experiments which explore atomic or optomechanical physics often rely on parametric or "sideband" interactions to achieve strong coupling between modes at different frequencies.1 By contrast, quantum optics experiments based on superconducting circuits most often employ resonant interactions to achieve strong coupling.2-4 While these techniques are reliable and well-understood, they are difficult to scale to more complex systems as they require either more physical wiring or sophisticated multiplexing of DC shift pulses. One way to avoid these difficulties is to engineer nonresonant parametric coupling in these systems. For instance, these techniques have been used to convert single microwave photons between different frequencies of a coplanar waveguide resonator, 5 and between a qubit and a linear mode.6,7 They have also been used to exchange coherent states between propagating modes at different frequencies,8 and between a cavity mode and the internal modes of a Josephson Ring Modulator.9 Here we extend these results by demonstrating parametric frequency conversion of coherent states between two spatially-distinct, three-dimensional cavity resonators. The use of nonresonant interactions implies the use of only static biasing fields and all-microwave frequency control pulses to switch the interactions on and off. Moreover, it allows for additional control over the coupling phase, as well as the ability to sequence coupling between any arbitrary pair of modes. This general approach possesses the potential to reduce wire count in quantum computing architectures since coupling in multi-mode systems can be frequency-multiplexed. Finally, this work demonstrates a methodology which may be useful in novel approaches to quantum computing that use linear modes for state storage.

Analysis of a parametrically driven exchange-type gate and a two-photon excitation gate between superconducting qubits

“…Moreover, the quest for useful quantum computations before full quantum error correction becomes available may be assisted by efficient, short-depth gate sequences based on two-or multi-qubit gates [14,15] with versatile types of interactions. In particular, parametric schemes based on tunable couplers have been proposed and recently realized as a means to achieve fast gates with high fidelities [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31].…”

Accelerated stabilization of coherent photon states

“…Several methods to tackle this trade-off have been demonstrated recently. These include the adjustment of the external quality factor of the storage resonator using a tunable coupler [10,11] or a flux-driven Josephson junction [12], and conversion from stationary to propagating photons using a driven transmon qubit [13] or a Josephson ring modulator [14].…”

“…Moreover, our stabilization method presents a complementary application for the tunable response rate of a resonator. Whereas recent experiments that have realized effectively tunable quality factors are motivated by fast injection of arbitrary photon states to the resonator [11][12][13], we envisage protocols where ancillary coherent states are repeatedly stabilized and reused for various tasks. On the other hand, in previous work [21] we have shown that maintaining a coherent state in this manner may be beneficial in reducing harmful heat loads subject to quantum circuits.…”

Hardware-Efficient and Fully Autonomous Quantum Error Correction in Superconducting Circuits

“…which does not conserve photon number [27][28][29], and couple each device via a similar coupling to a second, lossy degree of freedom, such as a rapidly decaying qubit or readout resonator, with a full example circuit shown in FIG. 1.…”

“…We couple the two devices via a high-frequency, driven coupling arXiv:1510.06117v1 [quant-ph] The two transmon qubits (blue boxes) are the good quantum degrees of freedom we wish to protect, and the two readout resonators (red boxes) are lossy objects we will use for error correction. The three driven SQUID couplings have precisely tuned flux biases (black circles) to enable parametric interactions, as discussed in the supplemental material.which does not conserve photon number [27][28][29], and couple each device via a similar coupling to a second, lossy degree of freedom, such as a rapidly decaying qubit or readout resonator, with a full example circuit shown in FIG. 1.…”