We propose protocols for entanglement generation between cavity-assisted quantum memories using weak bosonic coherent-states. Our protocols are shown to be near-deterministic in the low-loss regime and surpass the 50% success rate upper-bound for single-photon qubit encodings even with practical non-idealities, enabling an exponential rate scaling speed-up for the generation of multipartite entanglement.
We propose protocols for entanglement generation between cavity-assisted quantum memories using weak bosonic coherent-states. Our protocols are shown to be near-deterministic in the low-loss regime and surpass the 50% success rate upper-bound for single-photon qubit encodings even with practical non-idealities, enabling an exponential rate scaling speed-up for the generation of multipartite entanglement.
Entangling quantum memories, mediated by optical-frequency or microwave channels, at high rates and fidelities is key for linking qubits across short and long ranges. All well-known protocols encode up to one qubit per optical mode, entangling one pair of memory qubits per transmitted mode over the channel, with probability η, the channel’s transmissivity. The rate is proportional to η ideal Bell states (ebits) per mode. The quantum capacity, C(η)=−log2(1−η) ebits per mode, which ≈1.44η for high loss, thereby making these schemes near rate-optimal. However, C(η)→∞ as η→1, making the known schemes highly rate-suboptimal for shorter ranges. We propose a cavity-assisted memory–photon interface that can be used to entangle matter memories with Gottesman–Kitaev–Preskill (GKP) photonic qudits, which, along with dual-homodyne entanglement swaps that retain analog information, enables entangling memories at capacity-approaching rates at low loss. We benefit from the loss resilience of GKP-encoded states and the ability to encode multiple qubits in one mode. Our memory–photon interface further supports the preparation of needed ancilla GKP qudits. We expect our result to spur research in low-loss, high-cooperativity cavity-coupled qubits with high-efficiency optical coupling and demonstrations of high-rate short-range quantum links.
We investigate qubit entanglement dynamics in a two-qubit cavity system with stochastically fluctuating coupling strength, comparing white noise (Markovian) and Ornstein-Uhlenbeck noise (non-Markovian) processes. We analytically solve the system dynamics for both Fock and coherent cavity states and systematically characterize how initial qubit configurations affect entanglement generation and preservation. Our results reveal distinct dynamical regimes: in the Fock-state cavity, initial states in the single-excitation subspace generate robust qubit entanglement in decoherence-free subspaces, while initially entangled states in the double-excitation subspace exhibit inevitable decay without protective symmetries. For coherent cavities, we identify a critical photon-number threshold in the intermediate coherent-state amplitude regime where dynamics transition from low-frequency to high-frequency entanglement oscillations, while universal entanglement loss occurs at large amplitudes. Remarkable resilience against entanglement sudden death emerges under strong non-Markovian noise with long correlation times, where repeated revivals occur. These findings establish cavity photon statistics and environmental memory time as key control parameters for engineering qubit entanglement dynamics in qubit-cavity systems, revealing how system-environment correlations govern quantum information preservation.
Abstract The central technological appeal of quantum science resides in exploiting quantum effects, such as entanglement, for a variety of applications, including computing, communication and sensing 1 . The overarching challenge in these fields is to address, control and protect systems of many qubits against decoherence 2 . Against this backdrop, optical photons, naturally robust and easy to manipulate, represent ideal qubit carriers. However, the most successful technique so far for creating photonic entanglement 3 is inherently probabilistic and, therefore, subject to severe scalability limitations. Here we report the implementation of a deterministic protocol 4–6 for the creation of photonic entanglement with a single memory atom in a cavity 7 . We interleave controlled single-photon emissions with tailored atomic qubit rotations to efficiently grow Greenberger–Horne–Zeilinger (GHZ) states 8 of up to 14 photons and linear cluster states 9 of up to 12 photons with a fidelity lower bounded by 76(6)% and 56(4)%, respectively. Thanks to a source-to-detection efficiency of 43.18(7)% per photon, we measure these large states about once every minute, which is orders of magnitude faster than in any previous experiment 3,10–13 . In the future, this rate could be increased even further, the scheme could be extended to two atoms in a cavity 14,15 or several sources could be quantum mechanically coupled 16 , to generate higher-dimensional cluster states 17 . Overcoming the limitations encountered by probabilistic schemes for photonic entanglement generation, our results may offer a way towards scalable measurement-based quantum computation 18,19 and communication 20,21 .
Quantum entanglement between pairs of remote quantum memories (QMs) is a prerequisite for realizing many applications in quantum networks. Here, we present a heralded protocol for the parallel creation of quantum entanglement among multiple pairs of QMs placed in spatially separated nodes, where each QM, encoding a stationary qubit, couples to an optical cavity and deterministically interacts with single photons. Our protocol utilizes an entangled photon pair encoded in the high-dimensional time-bin degree of freedom to simultaneously entangle multiple QM pairs, and is efficient in terms of reducing the time consumption and photon loss during transmission. Furthermore, our approach can be extended to simultaneously support spatial-temporal multiplexing, as its success is heralded by the detection of single photons. These distinguishing features make our protocol particularly useful for long-distance quantum communication and large-scale quantum networks.
Parametrically driving an optical cavity that simultaneously couples to an atomic ensemble quantum memory enables in situ generation of multimode photon-memory entanglement. A high-rate bipartite photon-memory entanglement can be generated even after discarding one entangled optical mode. This protocol can be realized with existing technologies based on photonic resonators integrated with a rare-earth-ion doped quantum memory. The proposed scheme shows significant advantages in entanglement generation rates compared with prevailing quantum memory protocols and experiments, with theoretical ebit rates of tens of MHz without fine-tuned operating conditions. Such a photon-memory entanglement source offers a versatile resource for quantum networking and interconnect applications.