Deterministic Quantum State Transfer and Generation of Remote Entanglement using Microwave Photons (1712.08593v1)

Abstract: Sharing information coherently between nodes of a quantum network is at the foundation of distributed quantum information processing. In this scheme, the computation is divided into subroutines and performed on several smaller quantum registers connected by classical and quantum channels. A direct quantum channel, which connects nodes deterministically, rather than probabilistically, is advantageous for fault-tolerant quantum computation because it reduces the threshold requirements and can achieve larger entanglement rates. Here, we implement deterministic state transfer and entanglement protocols between two superconducting qubits fabricated on separate chips. Superconducting circuits constitute a universal quantum node capable of sending, receiving, storing, and processing quantum information. Our implementation is based on an all-microwave cavity-assisted Raman process which entangles or transfers the qubit state of a transmon-type artificial atom to a time-symmetric itinerant single photon. We transfer qubit states at a rate of $50 \, \rm{kHz}$ using the emitted photons which are absorbed at the receiving node with a probability of $98.1 \pm 0.1 \%$ achieving a transfer process fidelity of $80.02 \pm 0.07 \%$. We also prepare on demand remote entanglement with a fidelity as high as $78.9 \pm 0.1 \%$. Our results are in excellent agreement with numerical simulations based on a master equation description of the system. This deterministic quantum protocol has the potential to be used as a backbone of surface code quantum error correction across different nodes of a cryogenic network to realize large-scale fault-tolerant quantum computation in the circuit quantum electrodynamic architecture.

• The paper demonstrates a deterministic protocol for quantum state transfer, achieving 98.1% photon absorption and 80.02% fidelity in superconducting circuits.
• Utilizing a cavity-assisted Raman process, the study establishes direct quantum channels between remote transmon qubits at a 50 kHz rate.
• The results indicate significant progress towards scalable, fault-tolerant quantum computing by enabling robust remote entanglement generation.

Deterministic Generation of Remote Entanglement Using Microwave Photons

The paper "Deterministic Quantum State Transfer and Generation of Remote Entanglement Using Microwave Photons" presents a significant advancement in quantum information processing through the deterministic transfer of quantum states and generation of entanglement between remote quantum nodes. This research leverages superconducting qubits and employs microwave photons to establish direct quantum channels, a noteworthy stride towards scalable, fault-tolerant quantum computation.

Overview of the Methodology and Results

The authors implement a protocol based on the cavity-assisted Raman process, which facilitates the entanglement and transfer of quantum states via microwave photons between transmon-type artificial atoms. Utilizing superconducting circuits as universal quantum nodes, the process achieves a photon-mediated deterministic transfer of qubit states at a rate of 50 kHz, with a remarkable absorption probability of 98.1%. The fidelity of the state transfer process stands at 80.02%, while the on-demand generation of remote entangled states attains a fidelity of 78.9%. These values, supported by master equation simulations, are indicative of the precise control over quantum operations achieved in this paper.

Implications and Future Directions

This research has implications for the development of surface code quantum error correction in a network of cryogenic nodes. By ensuring high fidelity in both quantum state transfer and entanglement generation, the protocol contributes to the formation of a robust infrastructure for large-scale quantum computing. This deterministic protocol is in line with the requirements for realizing more complex quantum operations distributed across multiple nodes. Importantly, the paper illustrates the practicality of integrating deterministic quantum channels into existing quantum network architectures, fostering advancements in quantum communication and computation.

The scalability of this approach suggests that it could form the backbone of quantum networks designed for fault-tolerant distributed quantum computing. Enhancements in qubit coherence times and reductions in photon loss could potentially increase entanglement fidelities to levels sufficient for quantum error correction, such as the surface code.

Challenges and Future Prospects

While the results are promising, challenges remain in further reducing errors caused by photon loss and finite coherence times. These challenges highlight the need for advances in quantum hardware, particularly with respect to increasing transmon qubit coherence and optimizing the photon wavepacket shaping. The research sets the stage for exploring deterministic heralded remote entanglement, which could further enhance the protocol's applicability in more extensive quantum networks. Moreover, adapting this methodology to different quantum systems may present new opportunities in quantum information science.

Overall, the paper delineates an important step in bridging local quantum processors into an efficient and scalable quantum network, thereby contributing to the realization of distributed quantum computing systems. The deterministic nature of the process marks progress towards reliable entanglement distribution—an essential foundation for complex quantum algorithms and long-distance quantum communication.