We propose a proposal to generate scalable entanglement of remote material qubits via no-energy-exchange interactions with single photons. A strongly-coupled cavity quantum electrodynamics (CQED) system is arranged as a single-photon-level quantum router, which routes incoming photons to different outports based on the state of the involved material qubit. Two of the routers with qubits in their maximum superposition state are coupled together with a Mach-Zehnder-interferometer-like configuration. As a single photon transits through the system, we find the maximum entangled state between qubits is produced by finding a photon in the output mode. Remarkably, there is no energy exchanged between material qubits and photons. This ensures the possibility of purifying entangled states by using more photons in a physical situation, where loss and imperfections are inevitable. It also guarantees scalability in order to produce entanglement among multiple qubits without inducing incoherence caused by energy exchange. We analyzed the fidelity and probability of success for the proposed strongly-coupled CQED system. The expected maximum fidelity could reach over 0.9997 using only two photons in a technologically-feasible experiment. We also analyzed the scalability by providing examples for the generation of N-qubit entanglement and 3-qubit Greenberger-Horne-Zeilinger states based on the proposed technique. Our proposed method could be applied to create entanglement between multiple-node systems in a quantum network, or to generate special entangled state between remote material qubits, thereby testing the fundamentals of quantum mechanics.
We propose a proposal to generate scalable entanglement of remote material qubits via no-energy-exchange interactions with single photons. A strongly-coupled cavity quantum electrodynamics (CQED) system is arranged as a single-photon-level quantum router, which routes incoming photons to different outports based on the state of the involved material qubit. Two of the routers with qubits in their maximum superposition state are coupled together with a Mach-Zehnder-interferometer-like configuration. As a single photon transits through the system, we find the maximum entangled state between qubits is produced by finding a photon in the output mode. Remarkably, there is no energy exchanged between material qubits and photons. This ensures the possibility of purifying entangled states by using more photons in a physical situation, where loss and imperfections are inevitable. It also guarantees scalability in order to produce entanglement among multiple qubits without inducing incoherence caused by energy exchange. We analyzed the fidelity and probability of success for the proposed strongly-coupled CQED system. The expected maximum fidelity could reach over 0.9997 using only two photons in a technologically-feasible experiment. We also analyzed the scalability by providing examples for the generation of N-qubit entanglement and 3-qubit Greenberger-Horne-Zeilinger states based on the proposed technique. Our proposed method could be applied to create entanglement between multiple-node systems in a quantum network, or to generate special entangled state between remote material qubits, thereby testing the fundamentals of quantum mechanics.
We propose a scheme to entangle multiple material qubits through interaction with single photons via nonexciting processes associated with strongly coupling systems. The basic idea is based on the material state dependent reflection and transmission for the input photons. Thus, the material qubits in several systems can be entangled when one photon interacts with each system in cascade and the photon paths are mixed by the photon detection. The character of nonexciting of material qubits does not change the state of the material qubit and thus ensures the possibility of purifying entangled states by using more photons under realistic imperfect parameters. It also guarantees directly scaling up the scheme to entangle more qubits. Detailed analysis of fidelity and success probability of the scheme in the frame of an optical Fabry-P\'erot cavity based strongly coupling system is presented. It is shown that a two-qubit entangled state with fidelity above 0.99 is promised with only two photons by using currently feasible experimental parameters. Our scheme can also be directly implemented on other strongly coupled system.
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 .
Important tasks in cavity quantum electrodynamics include the generation and control of quantum states of spatially separated particles distributed in different cavities. An interesting question in this context is how to prepare entanglement among particles located in different cavities, which are important for large-scale quantum information processing. We here consider a multi-cavity system where cavities are coupled to a superconducting (SC) qubit and each cavity hosts many SC qubits. We show that all intra-cavity SC qubits plus the coupler SC qubit can be prepared in an entangled Greenberger–Horne–Zeilinger (GHZ) state, by using a single operation and without the need of measurements. The GHZ state is created without exciting the cavity modes; thus greatly suppressing the decoherence caused by the cavity-photon decay and the effect of unwanted inter-cavity crosstalk on the operation. We also introduce two simple methods for entangling the intra-cavity SC qubits in a GHZ state. As an example, our numerical simulations show that it is feasible, with current circuit-QED technology, to prepare high-fidelity GHZ states, for up to nine SC qubits by using SC qubits distributed in two cavities. This proposal can in principle be used to implement a GHZ state for an arbitrary number of SC qubits distributed in multiple cavities. The proposal is quite general and can be applied to a wide range of physical systems, with the intra-cavity qubits being either atoms, NV centers, quantum dots, or various SC qubits.
Typically, multipartite entangled coherent states are difficult to be extended and produced without measurement. We here propose a way to deterministically generate a GHZ (Greenberger–Horne–Zeilinger)-type entangled coherent state of cavities, utilizing a system consisting of a single superconducting qutrit (i.e., a three-level quantum system) and multiple microwave cavities. Due to the use of only a coupler qutrit, the architecture of the circuit system is quite simple. More importantly, our proposal does not require measurement on the state of qutrit compared with the previous proposals. Since the qutrit's third energy level is not populated during the operation, decoherence from the higher energy level is greatly minimized. Furthermore, the entire operation time is independent of the number of microwave cavities. As an example, our numerical simulations show that high-fidelity generation of a three-cavity GHZ-type entangled coherent state is feasible with present circuit quantum electrodynamics technology. This proposal is universal and can be applied to other physical systems, such as microwave or optical cavities, which are coupled to a single natural or artificial three-level atom.
We propose schemes for generating multiple-atom entangled states and a multiple-photon Greenberger-Horne-Zeilinger state, respectively, based on the input-output relation of the cavity. The numerical simulations show that produced multiple-particle entangled states have high fidelity even if the atoms are not localized in the Lamb-Dicke regime. Some practical quantum noises, such as atomic spontaneous emission and output coupling inefficiency, only decrease the success probability but exert no influence on the fidelity of prepared multiple-particle entangled states. The successful probabilities of our protocols approach unity in the ideal case. In addition, no need for individually addressing keeps the schemes easy to implement from the experimental point of view.
Hybrid entangled states are essential quantum resources not only for hybrid quantum communication but also for creating robust hybrid quantum networks and processors.By considering a circuit-cavity quantum electrodynamics (QED) system composed of a superconducting (SC) qutrit (a three-level quantum system) and n microwave cavities, we here present a method to prepare hybrid Greenberger-Horne-Zeilinger (GHZ) entangled states of n+1 qubits.The use of a single SC qutrit as the coupler leads to a significant saving in circuit hardware resources.The GHZ state preparation is deterministic without measurement.The operation time for the GHZ state preparation is independent of the number of qubits.Decoherence from the highest energy level of the SC qutrit is suppressed because this level remains unoccupied during the GHZ state preparation.Our numerical simulations demonstrate that the high-fidelity generation of hybrid GHZ states of an SC qubit and three photonic qubits is achievable within current circuit-QED technology.The proposed scheme possesses universality and is suitable for preparing hybrid GHZ states of a matter qubit (e.g., atomic qubit, trapped ion, quantum dot, magnon, NV center, and SC qubit with various types) and multiple photonic qubits across a wide range of physical systems.