Hyung Jin Yang

Quantum secure direct communication network with hyperentanglement

We propose a quantum secure direct communication protocol with entanglement swapping and hyperentanglement. Any two users, Alice and Bob, can communicate with each other in a quantum network, even though there is no direct quantum channel between them. The trust center, Trent, who provides a quantum channel to link them by performing entanglement swapping, cannot eavesdrop on their communication. This protocol provides a high channel capacity because it uses hyperentanglement, which can be generated using a beta barium borate crystal.

A Quantum Network System of QSS-QDC Using χ-Type Entangled States

A multiuser quantum direct communication network system for N users utilizing χ-type entangled states is proposed. The network system is composed of a communication center, N users, and N quantum lines linking the center and the N users. There is no quantum line among users, and therefore only N quantum lines are necessary for communication between users. Using one χ-type entangled state, in this protocol we are able to send two bits of information through direct communication and, at the same time, share two bits of quantum keys. The security of the protocol is then analyzed.

Bidirectional transfer of quantum information for unknown photons via cross-Kerr nonlinearity and photon-number-resolving measurement

We propose an arbitrary controlled-unitary (CU) gate and a bidirectional transfer scheme of quantum information (BTQI) for unknown photons. The proposed CU gate utilizes quantum non-demolition photon-number-resolving measurement based on the weak cross-Kerr nonlinearities (XKNLs) and two quantum bus beams; the proposed CU gate consists of consecutive operations of a controlled-path gate and a gathering-path gate. It is almost deterministic and is feasible with current technology when a strong amplitude of the coherent state and weak XKNLs are employed. Compared with the existing optical multi-qubit or controlled gates, which utilize XKNLs and homodyne detectors, the proposed CU gate can increase experimental realization feasibility and enhance robustness against decoherence. According to the CU gate, we present a BTQI scheme in which the two unknown states of photons between two parties (Alice and Bob) are mutually swapped by transferring only a single photon. Consequently, by using the proposed CU gate, it is possible to experimentally implement the BTQI scheme with a certain probability of success.

Analysis of optical parity gates of generating Bell state for quantum information and secure quantum communication via weak cross-Kerr nonlinearity under decoherence effect

We demonstrate the advantages of an optical parity gate using weak cross-Kerr nonlinearities (XKNLs), quantum bus (qubus) beams, and photon number resolving (PNR) measurement through our analysis, utilizing a master equation under the decoherence effect (occurred the dephasing and photon loss). To generate Bell states, parity gates based on quantum non-demolition measurement using XKNL are extensively employed in quantum information processing. When designing a parity gate via XKNL, the parity gate can be diversely constructed according to the measurement strategies. In practice, the interactions of XKNLs in optical fiber are inevitable under the decoherence effect. Thus, by our analysis of the decoherence effect, we show that the designed parity gate employing homodyne measurement would not be expected to provide reliable quantum operation. Furthermore, compared with a parity gate using a displacement operator and PNR measurement, we conclude there is experimental benefit from implementation of a parity gate via qubus beams and PNR measurement under the decoherence effect.

A Quantum Communication Protocol Transferring Unknown Photons Using Path-Polarization Hybrid Entanglement

We propose a protocol for transferring photons of unknown states to a distant location using path-polarization hybrid entanglement. Our protocol uses a polarizing beam splitter (PBS), a beam splitter (BS), a CNOT-operation, four unitary operations and polarizing detectors. In our protocol, the hybrid entangled states are generated by the PBS, and it is transmitted through the quantum channel containing the BS and CNOT-gate. The measurement results of the polarizing detectors and classical communications determine which unitary operation will be used in the last step for recovering initial states. The security of the channel in transmitting unknown photons between two parties is confirmed by the results of the measurement of each target photon in the control mode.

Quantum signature scheme based on a quantum search algorithm

We present a quantum signature scheme based on a two-qubit quantum search algorithm. For secure transmission of signatures, we use a quantum search algorithm that has not been used in previous quantum signature schemes. A two-step protocol secures the quantum channel, and a trusted center guarantees non-repudiation that is similar to other quantum signature schemes. We discuss the security of our protocol.

A Practical Approach Defeating Blackmailing

To simulate the functionalities of the real cash, one of the important requirements of electronic cash systems is the anonymity of users. Unconditional anonymity, however, is also very well suited to support criminals in blackmailing. Recently Kugler and Vogt [6] proposed a payment system based on the blind undeniable signature that protects the privacy of the users and defeats blackmailing with the assumption that the victim of a blackmailing can inform the Bank of a blackmailing before delivering the money and transfer the decryption key(i.e. the secret key of the victim) used in confirmation protocol without being detected by a blackmailer. But the assumption that the victim is always able to inform the bank of blackmailing is very impractical in such cases as kidnapping and special impersonation. In this paper, we propose two practical methods that gives the Bank the information about blackmailing and decryption key without any unpractical assumptions.

Controlled mutual quantum entity authentication using entanglement swapping

In this paper, we suggest a controlled mutual quantum entity authentication protocol by which two users mutually certify each other on a quantum network using a sequence of Greenberger–Horne–Zeilinger (GHZ)-like states. Unlike existing unidirectional quantum entity authentication, our protocol enables mutual quantum entity authentication utilizing entanglement swapping; moreover, it allows the managing trusted center (TC) or trusted third party (TTP) to effectively control the certification of two users using the nature of the GHZ-like state. We will also analyze the security of the protocol and quantum channel.

Optical scheme for generating hyperentanglement having photonic qubit and time-bin via quantum dot and cross-Kerr nonlinearity

We design an optical scheme to generate hyperentanglement correlated with degrees of freedom (DOFs) via quantum dots (QDs), weak cross-Kerr nonlinearities (XKNLs), and linearly optical apparatuses (including time-bin encoders). For generating hyperentanglement having its own correlations for two DOFs (polarization and time-bin) on two photons, we employ the effects of optical nonlinearities using a QD (photon-electron), a parity gate (XKNLs), and time-bin encodings (linear optics). In our scheme, the first nonlinear multi-qubit gate utilizes the interactions between photons and an electron of QD confined in a single-sided cavity, and the parity gate (second gate) uses weak XKNLs, quantum bus, and photon-number-resolving measurement to entangle the polarizations of two photons. Finally, for efficiency in generating hyperentanglement and for the experimental implementation of this scheme, we discuss how the QD-cavity system can be performed reliably, and also discuss analysis of the immunity of the parity gate (XKNLs) against the decoherence effect.

Controlled mutual quantum entity authentication with an untrusted third party

Abstract We propose a quantum control entity mutual authentication protocol that can be executed in environments involving an untrusted third party. In general, the third party, referred to as Charlie, can be an entity such as a telephone company, server, financial company, or login webpage for a portal service. Most communication protocols controlled by third parties are vulnerable to internal attacks. In this study, we present two solutions that make use of an entanglement correlation checking method and random numbers against an internal attack by an untrusted third party.