Qubits

Jie-Hui Huang, Shi-Yao Zhu

We investigate the monogamy nature of entanglement in a three-qubit system. A monogamy inequality is presented to describe the exclusive relation between the $A\text{\ensuremath{-}}B$ two-qubit concurrence ${C}_{AB}$ and the $AB\text{\ensuremath{-}}C$ three-qubit concurrence ${C}_{(AB)C}$, which represents the entanglement between qubits $\mathit{A}$ and $\mathit{B}$ as a whole and the third qubit $\mathit{C}$. It is found that the entanglement between any two qubits in a three-qubit system is limited by the entanglement between these two qubits and another qubit. As a consequence, we present the upper bounds for the concurrence ${C}_{AB}$, when the concurrence between qubits $\mathit{A}$ and $\mathit{C}$ $({C}_{AC})$ and the concurrence between qubits $\mathit{B}$ and $\mathit{C}$ $({C}_{BC})$ are both given or one of the two is provided.

Benjamin Bähr, Boris Lemmer, Rina Piccolo

Seongjeon Choi, Seok-Hyung Lee, Hyunseok Jeong

It was shown that using multiphoton qubits, a nearly deterministic Bell-state measurement can be performed with linear optics and on-off photodetectors [Phys. Rev. Lett. 114, 113603 (2015)]. However, multiphoton qubits are generally more fragile than single-photon qubits under a lossy environment. In this paper, we propose and analyze a scheme to teleport multiphoton-qubit information using hybrid entanglement with a loss-tolerant carrier qubit. We consider three candidates for the carrier qubit: a coherent-state qubit, a single-photon polarization qubit, and a vacuum-and-single-photon qubit. We find that teleportation with the vacuum-and-single-photon qubit tolerates about 10 times greater photon losses than with the multiphoton qubit of the photon number $N\ensuremath{\ge}4$ in the high fidelity regime ($F\ensuremath{\ge}90%$). The coherent-state qubit encoding may be even better than the vacuum-and-single-photon qubit as the carrier when its amplitude is as small as $\ensuremath{\alpha}<0.78$. We further point out that the fidelity of the teleported state by our scheme is determined by loss in the carrier qubit while the success probability depends on loss only in the multiphoton qubit to be teleported. Our study implies that the hybrid architecture may complement the weaknesses of each qubit encoding.

I Gst. Ag. Anom Trenggana Dharastika

Pada tugas akhir ini telah dirumuskan persamaan umum teleportasi kuantum qubit tunggal sembarang melalui qubit rangkap tiga. Dalam perumusannya digunakan bentuk umum dari qubit rangkap tiga sebagai saluran pengiriman qubit tunggal sembarang, sehingga berdasarkan perumusan tersebut dapat diperoleh qubit rangkap tiga yang mampu mengirim qubit tunggal sembarang. Qubit rangkap tiga dapat diklasifikasikan kedalam enam kelas yaitu A-B-C, A-BC, B-AC, C-AB, GHZ, dan W. Diantara keenam kelas tersebut hanya kelas A-B-C dan kelas C-AB yang tidak mampu mengirimkan qubit tunggal sembarang, sehingga dapat dikatakan bahwa qubit rangkap tiga yang mampu mengirim qubit tunggal sembarang adalah qubit rangkap tiga yang memiliki hubungan keterbelitan antara pengirim dan penerima. Selain itu diperoleh juga hasil bahwa qubit tunggal sembarang dapat dikirim dengan qubit rangkap tiga dalam keadaan khusus. ================================================================= In this final project, a general equation has been formulated quantum teleportation for single arbitrary qubit through triple qubit. In the formulation, general form of triple qubit is used as the transmission canal to send single arbitrary qubit thus based on the formulation can be obtained triple qubit that capable of sending single arbitrary qubit. Triple qubit can be classified into six class which are A-B-C, A-BC, B-AC, C-AB, GHZ, and W. Among the six class only class A-B-C and class C- AB are not capable to send single arbitrary qubit, thus can be conclude that triple qubit that capable to send single arbitrary qubit are the one that have relation of entanglement between sender and receiver. It also been found that single arbitrary qubit can be sent through triple qubit with special condition.