Algorithmic cooling based on cross-relaxation and decoherence-free subspace
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July 2020 Vol. 63 No. 7: 270311 https://doi.org/10.1007/s11433-019-1492-4
Algorithmic cooling based on cross-relaxation and decoherence-free subspace HengYan Wang1, Jian Pan2,3,4, WenQiang Zheng5* , and XinHua Peng2,3,4* 1 Department
of Physics, Zhejiang University of Science and Technology, Hangzhou 310023, China; National Laboratory for Physical Sciences at the Microscale, Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China; 3 CAS Key Laboratory of Microscale Magnetic Resonance, University of Science and Technology of China, Hefei 230026, China; 4 Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, China; 5 Collaborative Innovation Center for Bio-Med Physics Information Technology, College of Science, Zhejiang University of Technology, Hangzhou 310023, China 2 Hefei
Received September 27, 2019; accepted December 10, 2019; published online March 26, 2020
Heat-bath algorithmic cooling (HBAC) has been proven to be a powerful and effective method for obtaining high polarization of the target system. Its cooling upper bound has been recently found using a specific algorithm, the partner pairing algorithm (PPAHBAC). It has been shown that by including cross-relaxation, it is possible to surpass the cooling bounds. Herein, by combining cross-relaxation and decoherence-free subspace, we present a two-qubit reset sequence and then generate a new algorithmic cooling (AC) technique using irreversible polarization compression to further surpass the bound. The proposed two-qubit reset sequence can prepare one of the two qubits to four times the polarization of a single-qubit reset operation in PPA-HBAC for low polarization. When the qubit number is large, the cooling limit of the proposed AC is approximately five times as high as the PPA-HBAC. The results reveal that cross-relaxation and decoherence-free subspace are promising resources to create new AC for higher polarization. algorithmic cooling, polarization enhancing, cross-relaxation, decoherence-free subspace PACS number(s): Citation:
03.65.Yz, 03.67.Ac, 82.56.Na, 33.25.+k
H. Y. Wang, J. Pan, W. Q. Zheng, and X. H. Peng, Algorithmic cooling based on cross-relaxation and decoherence-free subspace, Sci. China-Phys. Mech. Astron. 63, 270311 (2020), https://doi.org/10.1007/s11433-019-1492-4
1 Introduction Enhancing the polarization is of great significance to quantum information technology. For example, effectively enhancing the polarization can improve the signal-to-noise ratio (SNR) in spectroscopy [1, 2] and provide a potential solution to overcome the scalable problem [3] for many quantum computation systems such as NMR and ESR [4-6]. More*Corresponding authors (WenQiang Zheng, email: [email protected]; XinHua Peng, email: [email protected])
over, polarization enhancement can help to prepare ancilla qubits in highly pure states for quantum error correction [7]. The polarization of one qubit is defined as th
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