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Density matrix, which characterizes a quantum state, plays an important role in quantum mechanics. Recently, a method which can directly measure the elements of a density matrix was proposed. Compared with the conventional quantum state tomography which is widely used to reconstruct the density matrix, this measurement method has the advantages of directness and simplicity. However, this direct measurement method relies on an extra pointer space. The addition of this extra pointer can increase the complexity of an experiment. In this paper, we first review previous work on direct measurement, then we propose a scheme to directly measure the density matrix based on δ-quench, which is also a direct measurement method but needs no additional pointer. This proposal reduces the complexity of the measuring system and further simplifies the measurement. We propose two schemes to realize this δ-quench measurement, then analyse their superiorities in different situations of measurement. An experiment to measure photon's density matrix is also designed.
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Keywords:
- quantum measurement /
- density matrix /
- direct measurement
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[28] Pan W W, Xu X Y, Kedem Y, Wang Q Q, Chen Z, Jan M, Su K, Xu J S, Han Y J, Li C F, Guo G C 2019 Phys. Rev. Lett. 123 150402Google Scholar
[29] Thekkadath G S, Giner L, Chalich Y, Horton M J, Banker J, Lundeen J S 2016 Phys. Rev. Lett. 117 120401Google Scholar
[30] Calderaro L, Foletto G, Dequal D, Villoresi P, Vallone G 2018 Phys. Rev. Lett. 121 230501Google Scholar
[31] Zhang S, Zhou Y, Mei Y, Liao K, Wen Y L, Li J, Zhang X D, Du S, Yan H, Zhu S L 2019 Phys. Rev. Lett. 123 190402Google Scholar
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[1] James D F V, Kwiat P G, Munro W J, White A G 2001 Phys. Rev. A 64 052312Google Scholar
[2] Schmied R 2016 J. Mod. Opt. 63 1744Google Scholar
[3] Lorenzo A D 2013 Phys. Rev. Lett. 110 010404Google Scholar
[4] Lorenzo A D 2013 Phys. Rev. A 88 042114Google Scholar
[5] Bent N, Qassim H, Tahir A A, Sych D, Leuchs G, Sánchez-Soto L L, Karimi E, Boyd R W 2015 Phys. Rev. X 5 041006
[6] Lundeen J S, Sutherland B, Patel A, Stewart C, Bamber C 2011 Nature 474 188Google Scholar
[7] Aharonov Y, Albert D Z, Vaidman L 1988 Phys. Rev. Lett. 60 1351Google Scholar
[8] Dressel J, Malik M, Miatto F M, Jordan A N, Boyd R W 2014 Rev. Mod. Phys. 86 307Google Scholar
[9] Ritchie N W M, Story J G, Hulet R G 1991 Phys. Rev. Lett. 66 1107Google Scholar
[10] Yang G, Lian B W, Nie M 2016 Chin. Phys. B 25 080310Google Scholar
[11] Liao X P, Fang M F, Fang J S, Zhu Q Q 2013 Chin. Phys. B 23 020304
[12] 黄江 2017 物理学报 66 010301Google Scholar
Huang J 2017 Acta Phys. Sin. 66 010301Google Scholar
[13] 王美姣, 夏云杰 2015 物理学报 64 240303Google Scholar
Wang M J, Xia Y J 2015 Acta Phys. Sin. 64 240303Google Scholar
[14] Salvail J Z, Agnew M, Johnson A S, Bolduc E 2013 Nat. Photonics 7 316Google Scholar
[15] Malik M, Mirhosseini M, Lavery M P J, Leach J, Padgett M J, Boyd R W 2014 Nat. Commun. 5 3115Google Scholar
[16] Kocsis S, Braverman B, Ravets S, Stevens M J, Mirin R P, Shalm L K, Steinberg A M 2011 Science 332 1170Google Scholar
[17] Lundeen J S, Bamber C 2012 Phys. Rev. Lett. 108 070402Google Scholar
[18] Boldu E, Gariepy G, Leach J 2016 Nat. Commun. 7 10439Google Scholar
[19] Qin L, Xu L, Feng W, Li X Q 2017 New J. Phys. 19 033036Google Scholar
[20] Bamber C, Lundeen J S 2014 Phys. Rev. Lett. 112 070405Google Scholar
[21] Shojaee E, Jackson C S, Riofrío C A, Kalev A, Deutsch I H 2018 Phys. Rev. Lett. 121 130404Google Scholar
[22] Fischbach J, Freyberger M 2012 Phys. Rev. A 86 052110Google Scholar
[23] Mirhosseini M, Magana-Loaiza O S, Rafsanjani S M H, Boyd R W 2014 Phys. Rev. Lett. 113 090402Google Scholar
[24] Vallone G, Dequal D 2016 Phys. Rev. Lett. 116 040502Google Scholar
[25] Denkmayr T, Geppert H, Lemmel H, Waegell M, Dressel J, Hasegawa Y, Sponar S 2018 Phys. Rev. Lett. 118 010402
[26] Zhang C R, Hu M J, Xiang G Y, Zhang Y S, Li C F, Guo G C 2020 Chin. Phys. Lett. 37 080301Google Scholar
[27] Zhang C R, Hu M J, Hou Z B, Tang J F, Zhu J, Xiang G Y, Li C F, Guo G C, Zhang Y S 2020 Phys. Rev. A 101 012119Google Scholar
[28] Pan W W, Xu X Y, Kedem Y, Wang Q Q, Chen Z, Jan M, Su K, Xu J S, Han Y J, Li C F, Guo G C 2019 Phys. Rev. Lett. 123 150402Google Scholar
[29] Thekkadath G S, Giner L, Chalich Y, Horton M J, Banker J, Lundeen J S 2016 Phys. Rev. Lett. 117 120401Google Scholar
[30] Calderaro L, Foletto G, Dequal D, Villoresi P, Vallone G 2018 Phys. Rev. Lett. 121 230501Google Scholar
[31] Zhang S, Zhou Y, Mei Y, Liao K, Wen Y L, Li J, Zhang X D, Du S, Yan H, Zhu S L 2019 Phys. Rev. Lett. 123 190402Google Scholar
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