Experimental Realization of One-Way Quantum Computing with Two-Photon Four-Qubit Cluster States

Abstract

We report an experimental realization of one-way quantum computing on a two-photon four-qubit cluster state. This is accomplished by developing a two-photon cluster state source entangled both in polarization and spatial modes. With this special source, we implemented a highly efficient Grover's search algorithm and high-fidelity two qubits quantum gates. Our experiment demonstrates that such cluster states could serve as an ideal source and a building block for rapid and precise optical quantum computation.PACS numbers: 03.67. Lx, 03.67.Mn, 42.50.Dv Highly entangled multipartite states, so-called cluster states, have recently raised enormous interest in quantum information processing (QIP). These sorts of states are crucial as a fundamental resource and a building block aimed at one-way universal quantum computing [1]. They are also essential elements for various quantum error correction codes and quantum communication protocols [2]. Moreover, the entanglements are shown to be robust against decoherence [3], and persistent against loss of qubits [1], and thus are exceptionally well suited for quantum computing and many tasks [1,2]. Considerable efforts have been made toward generating and characterizing cluster state in linear optics [4,5,6,7,8,9]. Recently the principal feasibility of a one-way quantum computing model has been experimentally demonstrated through 4-photon cluster states successfully [7,8,10].So far, preparing photonic cluster state still suffers from several serious limitations. Due to the probabilistic nature and Poissonian distribution of the parametric down-conversion process, the generation rate of 4-photon cluster states is quite low [5,6,7,8], and largely restricts speed of computing. Besides, the quality and fidelity of prepared cluster states are relatively low [6,7,8], which are difficult to be improved substantially. These disadvantages consequently impose great challenges of advancement even for few-qubit quantum computing.Fortunately, motivated by the progress that an important type of states termed hyper-entangled states have been experimentally generated [11,12,13,14], we have the possibility to produce a new type of cluster state (2-photon 4-qubit cluster state) with nearly perfect fidelity and high generation rate. The hyper-entangled states have been used to test "All-Versus-Nothing" (AVN) quantum nonlocality [11,12,15], and are shown to lead to an enhancing violation of local realism [16,17]. The states also enable to perform complete deterministic Bell state analysis [18] as demonstrated in [14,19].In this Letter we report an experimental realization of one-way quantum computing with such a 2-photon 4-qubit cluster state. The key idea is to develop and employ a bright source which produces a 2-photon state entangled both in polarization and spatial modes. We are thus able to implement the Grover's algorithm and quantum gates with excellent performances. The genuine four-partite entanglement and high fidelity of better than 88% are characterized by an optimal entanglement w...

Gates for one-way quantum computation based on Einstein-Podolsky-Rosen entanglement

“…Due to the role of measurements the QC based on cluster entanglement is essentially irreversible, and thus it is named the one-way QC [3]. The one-way QC was first experimentally demonstrated with a four-qubit cluster state of single photons [4][5][6]. In the meanwhile, an universal QC model using continuous-variable (CV) cluster states was proposed [7].…”

Pure-state tomography with the expectation value of Pauli operators

“…The red squre represents fidelity of reconstruction using our protocol. Figure 7 depicts a typical scheme for measuring a polarization-encoded n-photon state [19][20][21][22][23][24]. Quarter-and half-waveplates in each photon's path are rotated to choose a separable polarization basis.…”

Experimental Engineering of Photonic Quantum Entanglement

“…However, it has also been discovered that a scalable quantum computer can in principle be realized by using only single-photon sources, linear-optics elements and single-photon detectors (Knill et al (2001)). Several proof-of-principle demonstrations for linear optical quantum computing have been given, including controlled-NOT gates (Gasparoni et al (2004); O'Brien et al (2003); ; Sanaka et al (2004)), Grover's search algorithm (Grover (1997); Kwiat et al (2000); Prevedel et al (2007)), Deutsch-Josza algorithm (Deutsch (1985); Tame et al (2007)), Shor's factorization algorithm (Lanyon et al (2007); ; Politi et al (2009)) and the promising and new model of the one-way quantum computation (Chen et al (2007); Kiesel et al (2005); Prevedel et al (2007); Vallone et al (2008);Walther et al (2005)). A main issue on the path of photonic quantum information processing is that the best current photon source, SPDC, is a process where the photons are created at random times (Zukowski et al (1993)).…”