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1. Joint Turbo Receiver for LDPC-Coded MIMO Systems Based on Semi-definite Relaxation

   Wang, K.; Ding, Z. (August 2018, IEEE Vehicular Technology Conference)

   Semi-definite relaxation (SDR) has demonstrated the capability of approaching maximum-likelihood (ML) performance. In this work, we first develop a new SDR-based detector that exploits forward error correction (FEC) code information in the detection stage. The joint SDR detector substantially improves overall receiver performance by generating highly reliable information to downstream decoder. For further performance improvement, we integrate the joint SDR detector with decoder using a feedback link to form an iterative turbo receiver. Meanwhile, we propose a simplified SDR receiver that solves only one SDR problem per codeword instead of solving multiple SDR problems in the iterative turbo processing. This simplification significantly reduces the complexity of SDR turbo receiver, while maintaining a similarly superior error performance. 

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2. Comparing Shor and Steane error correction using the Bacon-Shor code

   https://doi.org/10.1126/sciadv.adp2008  

   Huang, Shilin; Brown, Kenneth R; Cetina, Marko (November 2024, Science Advances)

   Quantum states decohere through interaction with the environment. Quantum error correction can preserve coherence through active feedback wherein quantum information is encoded into a logical state with a high degree of symmetry. Perturbations are detected by measuring the symmetries of the state and corrected by applying gates based on these measurements. To measure the symmetries without perturbing the data, ancillary quantum states are required. Shor error correction uses a separate quantum state for the measurement of each symmetry. Steane error correction maps the perturbations onto a logical ancilla qubit, which is then measured to check several symmetries simultaneously. We experimentally compare Shor and Steane correction of bit flip errors using the Bacon-Shor code implemented in a chain of 23 trapped atomic ions. We find that the Steane method produces fewer errors after a single round of error correction and less disturbance to the data qubits without error correction. 

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3. Proactive Anti-Eavesdropping With Trap Deployment in Wireless Networks

   https://doi.org/10.1109/TDSC.2022.3141406  

   He, Qiuye; Fang, Song; Wang, Tao; Liu, Yao; Zhao, Shangqing; Lu, Zhuo (January 2022, IEEE Transactions on Dependable and Secure Computing)

   Due to the open nature of wireless medium, wireless communications are especially vulnerable to eavesdropping attacks. This paper designs a new wireless communication system to deal with eavesdropping attacks. The proposed system can enable a legitimate receiver to get desired messages and meanwhile an eavesdropper to hear ``fake" but meaningful messages by combining confidentiality and deception, thereby confusing the eavesdropper and achieving additional concealment that further protects exchanged messages. Towards this goal, we propose techniques that can conceal exchanged messages by utilizing wireless channel characteristics between the transmitter and the receiver, as well as techniques that can attract an eavesdropper to gradually approach a trap region, where the eavesdropper can get fake messages. We also provide both theoretical and empirical analysis of the established secure channel between the transmitter and the receiver. We develop a prototype system using Universal Software Defined Radio Peripherals (USRPs)Experimental results show that an eavesdropper at a trap location can receive fake information with a bit error rate (BER) close to 0, and the transmitter with multiple antennas can successfully deploy a trap area. 

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4. On mitigation of pilot spoofing attack

   https://doi.org/10.1109/ICASSP.2017.7952526  

   Tugnait, Jitendra K. (March 2017, 2017 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP))

   In a time-division duplex (TDD) multiple antenna system, the channel state information (CSI) can be estimated using reverse training. A pilot contamination (spoofing) attack occurs when during the training phase, an adversary also sends identical training (pilot) signal as that of the legitimate receiver. This contaminates channel estimation and alters the legitimate beamformimg design, facilitating eavesdropping. A recent approach proposed superimposing a random sequence on the training sequence at the legitimate receiver and then using the minimum description length (MDL) criterion to detect pilot contamination attack. In this paper we augment this approach with joint estimation of both legitimate receiver and eavesdropper channels, and secure beamforming, to mitigate the effects of pilot spoofing. The proposed mitigation approach is illustrated via simulations. 

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5. Autonomous error correction of a single logical qubit using two transmons

   https://doi.org/10.1038/s41467-024-45858-z  

   Li, Ziqian; Roy, Tanay; Rodríguez Pérez, David; Lee, Kan-Heng; Kapit, Eliot; Schuster, David I. (February 2024, Nature Communications)

   Abstract Large-scale quantum computers will inevitably need quantum error correction to protect information against decoherence. Traditional error correction typically requires many qubits, along with high-efficiency error syndrome measurement and real-time feedback. Autonomous quantum error correction instead uses steady-state bath engineering to perform the correction in a hardware-efficient manner. In this work, we develop a new autonomous quantum error correction scheme that actively corrects single-photon loss and passively suppresses low-frequency dephasing, and we demonstrate an important experimental step towards its full implementation with transmons. Compared to uncorrected encoding, improvements are experimentally witnessed for the logical zero, one, and superposition states. Our results show the potential of implementing hardware-efficient autonomous quantum error correction to enhance the reliability of a transmon-based quantum information processor. 

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