Large-scale fault-tolerant superconducting quantum computation needs rapid quantum communication to network qubits fabricated on different chips and long-range couplers to implement efficient quantum error correction codes. Quantum channels used for these purposes are best modeled by multimode resonators, which lie between single-mode cavities and waveguides with a continuum of modes. In this Letter, we propose a non-Markovian formalism for quantum state transfer using coupling strengths comparable to the channel's free spectral range (g∼Δ_{FSR}). Our scheme merges features of both the stimulated-Raman-adiabatic-passage-based methods for single-mode cavities and the pitch-and-catch protocol for long waveguides, integrating their advantages of low loss and high speed. It is immune to thermal channel occupations if using harmonic resonators for the sender and receiver.
Large-scale fault-tolerant superconducting quantum computation needs rapid quantum communication to network qubits fabricated on different chips and long-range couplers to implement efficient quantum error correction codes. Quantum channels used for these purposes are best modeled by multimode resonators, which lie between single-mode cavities and waveguides with a continuum of modes. In this Letter, we propose a non-Markovian formalism for quantum state transfer using coupling strengths comparable to the channel's free spectral range (g∼Δ_{FSR}). Our scheme merges features of both the stimulated-Raman-adiabatic-passage-based methods for single-mode cavities and the pitch-and-catch protocol for long waveguides, integrating their advantages of low loss and high speed. It is immune to thermal channel occupations if using harmonic resonators for the sender and receiver.
Superconducting quantum computing emerges as one of the leading candidates for achieving quantum advantage. However, a prevailing challenge is the coding overhead due to limited quantum connectivity, constrained by nearest-neighbor coupling among superconducting qubits. Here, we propose a novel multimode coupling scheme using three resonators driven by two microwaves, based on the resonator-induced phase gate, to extend the ZZ interaction distance between qubits. We demonstrate a controlled-Z (cz) gate fidelity exceeding 99.9% within 160 ns at a free spectral range (FSR) of 1.4 GHz, and by optimizing driving pulses, we further reduce the residual photon to nearly 10^{-3} within 100 ns at a FSR of 0.2 GHz. These facilitate the long-range cz gate over separations reaching submeters, thus significantly enhancing qubit connectivity and making a practical step toward the scalable integration and modularization of quantum processors. Specifically, our approach supports the implementation of quantum error correction codes requiring high connectivity, such as low-density parity check codes that pave the way to achieving fault-tolerant quantum computing.
Quantum state transfer between distant nodes is essential for distributed quantum information processing. Existing protocols are typically optimized for specific coupling regimes, such as adiabatic dark-state transfer in the single-mode limit and pitch-and-catch schemes in the multimode regime, leaving the crossover between them without a simple and unified control strategy. Here we identify a minimal two-parameter control framework that enables high-fidelity quantum state transfer across this single-mode-to-multimode crossover in a multimode quantum channel. Using a pulse-shaped pitch-and-catch protocol controlled only by the pulse ramp rate and the emission-absorption delay, we achieve transfer fidelities exceeding 99.9%, extending pitch-and-catch protocols toward the single-mode limit without requiring dark-state protection or complex pulse design. We further demonstrate robustness against dissipation, disorder, detuning, and imperfect initialization under experimentally realistic conditions. These results provide a simple and broadly applicable framework for state transfer in multimode quantum channels, with relevance to circuit-QED and hybrid quantum-acoustic systems.
We propose an efficient scheme for the implementation of quantum information transfer in a one-dimensional coupled resonator waveguide. We show that, based on the effective long-range dipole-dipole interactions between the atoms mediated by the cavity modes, Raman transitions between the atoms trapped in different nodes can take place. Quantum information could be transferred directly between the opposite ends of the coupled waveguide without involving the intermediate nodes via either Raman transitions or the stimulated Raman adiabatic passages. Since this scheme, in principle, is a one-step protocol, it may provide useful applications in quantum communications.
Achieving high-fidelity direct two-qubit gates over meter-scale quantum interconnects is challenging, in part due to the multimode nature of such systems. One alternative scheme is to combine local operations with remote quantum state transfer or remote entanglement. Here, we theoretically study quantum state transfer and entanglement generation for two distant qubits, equipped with tunable interactions, over a common multimode interconnect. We model the performance of the superadiabatic transitionless driving (SATD) protocol for adiabatic passage and demonstrate various favorable improvements over the standard method. In particular, by suppressing leakage to a select (resonant) interconnect mode, SATD breaks the speed-limit relation imposed by the qubit-interconnect interaction g, where instead the operation time is limited by leakage to the adjacent modes, i.e., the free spectral range ${\mathrm{\ensuremath{\Delta}}}_{c}$ of the interconnect, allowing for fast operations even with weak g. Furthermore, we identify a multimode error mechanism for Bell-state generation using such adiabatic protocols, in which the even/odd modal dependence of qubit-interconnect interaction breaks down the dark-state symmetry, leading to detrimental adiabatic overlap with the odd modes growing as $(g/{\mathrm{\ensuremath{\Delta}}}_{c}{)}^{2}$. Therefore, adopting a weak coupling, imposed by a multimode interconnect, SATD provides a significant improvement in terms of operation speed and consequently sensitivity to incoherent error.
The main challenge in deterministic quantum state transfer in long-distance quantum communications is the transmission losses in the communication channel. To overcome this limitation, here we use the adiabatic theorem and find a lossless evolution path between two remote mechanical modes. By adiabatic variation of the effective coupling strengths between the two nodes and the intermediate optical channel modes, we engineer a transmission path for the quantum state transfer that is decoupled from the decaying fiber modes. Using our proposed method we show that one obtains a quantum state transfer with high efficiency. Furthermore, to bypass the slow nature of the adiabatic process and its sensitivity to the mechanical damping and noise as well as the strength of the driving pulses, we develop the shortcut to adiabatic passage protocol for our proposed quantum state transfer. Our results show that the shortcut to adiabaticity provides an efficient and fast quantum state transfer even for small values of the coupling strength. We show that the performance of our protocol for long-distance quantum communications remains efficient for transferring the quantum states between two remote mechanical resonators being hundred meters apart.
Performing a faithful transfer of an unknown quantum state is a key challenge for enabling quantum networks. The realization of networks with a small number of quantum links is now actively pursued, which calls for an assessment of different state transfer methods to guide future design decisions. Here, we theoretically investigate quantum state transfer between two distant qubits, each in a cavity, connected by a waveguide, e.g., an optical fiber. We evaluate the achievable success probabilities of state transfer for two different protocols: standard wave packet shaping and adiabatic passage. The main loss sources are transmission losses in the waveguide and absorption losses in the cavities. While special cases studied in the literature indicate that adiabatic passages may be beneficial in this context, it remained an open question under which conditions this is the case and whether their use will be advantageous in practice. We answer these questions by providing a full analysis, showing that state transfer by adiabatic passage—in contrast to wave packet shaping—can mitigate the effects of undesired cavity losses, far beyond the regime of coupling to a single waveguide mode and the regime of lossless waveguides, as was proposed so far. Furthermore, we show that the photon arrival probability is in fact bounded in a trade-off between losses due to non-adiabaticity and due to coupling to off-resonant waveguide modes. We clarify that neither protocol can avoid transmission losses and discuss how the cavity parameters should be chosen to achieve an optimal state transfer.