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Volumn 71, Issue 3, 2005, Pages

Synthesizing arbitrary two-photon polarization mixed states

Author keywords

[No Author keywords available]

Indexed keywords

POLARIZATION MIXED STATES; QUANTUM ERRORS; QUANTUM-INFORMATION PROCESSING (QIP); SPONTANEOUS PARAMETERIC DOWN-CONVERSION (SPDC);

EID: 18444387094     PISSN: 10502947     EISSN: 10941622     Source Type: Journal    
DOI: 10.1103/PhysRevA.71.032329     Document Type: Article
Times cited : (47)

References (47)
  • 6
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    • P. G. Kwiat et al., e-print quant-ph/0303040
    • N. A. Peters et al., Phys. Rev. Lett. 92, 133601 (2004). P. G. Kwiat et al., e-print quant-ph/0303040.
    • (2004) Phys. Rev. Lett. , vol.92 , pp. 133601
    • Peters, N.A.1
  • 9
    • 4143119232 scopus 로고    scopus 로고
    • which uses down-conversion, beam splitters, and single-mode fibers to accomplish arbitrary two-photon polarization mixed states. However, that scheme requires coupling of four spatial modes into a single-mode fiber. This is necessarily a nonunitary (and very lossy) process, so that the desired two-qubit states are only generated for a small fraction, since the postselected ensemble is much smaller (by a factor of 16) than the ensemble of emitted pairs. The methods described in the present paper do not require such postselection
    • We learned recently of a related work by C. Zhang, Phys. Rev. A 69, 014304 (2004), which uses down-conversion, beam splitters, and single-mode fibers to accomplish arbitrary two-photon polarization mixed states. However, that scheme requires coupling of four spatial modes into a single-mode fiber. This is necessarily a nonunitary (and very lossy) process, so that the desired two-qubit states are only generated for a small fraction, since the postselected ensemble is much smaller (by a factor of 16) than the ensemble of emitted pairs. The methods described in the present paper do not require such postselection.
    • (2004) Phys. Rev. A , vol.69 , pp. 014304
    • Zhang, C.1
  • 10
    • 18444413782 scopus 로고    scopus 로고
    • note
    • P〉 is a straightforward procedure of unitary operations. However, such efficient entangling gates for photon polarizations are not yet available. See also [11].
  • 11
    • 0242442577 scopus 로고    scopus 로고
    • However, recently nondeterministic CNOT gates for photon polarizations have been achieved using a postselection method. See, e.g., T. B. Pittman, M. J. Fitch, B. C. Jacobs, and J. D. Franson, Phys. Rev. A 68, 032316 (2003);
    • (2003) Phys. Rev. A , vol.68 , pp. 032316
    • Pittman, T.B.1    Fitch, M.J.2    Jacobs, B.C.3    Franson, J.D.4
  • 20
    • 18444388952 scopus 로고    scopus 로고
    • note
    • 2/Δλ. For example, for 700 nm photons with 1 nm (5 nm) bandpass interference filters, the coherence length is roughly 500 urn (100 μm).
  • 21
    • 0031485474 scopus 로고    scopus 로고
    • As the opening angle in our down-conversion is small and fixed at ∼3°, we have ignored the effect of variation in polarization direction as the scattering angle varies, the variation being dramatic at large angles. For discussions of this effect, see A. Migdall, J. Opt. Soc. Am. B 14, 1093 (1997).
    • (1997) J. Opt. Soc. Am. B , vol.14 , pp. 1093
    • Migdall, A.1
  • 23
    • 18444381559 scopus 로고    scopus 로고
    • note
    • 0)L/\λ, where L is the thickness of the crystal and λ is the wavelength of light. Retardances that differ by an integer give a phase of multiples of 2π. A true zero-order wave plate has retardance usually less than 1, but is usually too thin for practical use. A multiorder wave plate has δ>1, and is therefore more sensitive to variations in the wavelength. A compound zero-order wave plate is composed of two multiorder wave plates with their optic axes orthogonal to each other such that the net retardance is less than 1. Hence, compound zero-order wave plates are less sensitive to wavelength than are multiorder wave plates (but more sensitive to alignment and beam noncollimation). See, e.g., http://www.meadowlark.com/AppNotes/, Meadowlark Optics, Inc., 2003 (unpublished).
  • 25
    • 18444363439 scopus 로고    scopus 로고
    • note
    • The local unitary transformations at each stage can be calculated backward, starting with those at the fourth set of crystals. The unitary transformations caused by the nonlinear crystals themselves can be compensated by modifying the local unitary transformations. Decoherence effects arising from wave plates and crystals are assumed to be negligible.
  • 27
    • 18444396370 scopus 로고    scopus 로고
    • note
    • U,loss〉+|ψL,loss〉. This loss is of no consequence in practice, as the pump contains large numbers of photons, and the creation of a particular two-photon state will be postselected by coincidence counts.
  • 28
    • 18444390051 scopus 로고    scopus 로고
    • note
    • 2/2].
  • 29
    • 18444400342 scopus 로고    scopus 로고
    • note
    • One can argue that the state (10) is a purification of the mixed state, with the "ancillas" being the timing information; see also remarks in [10].
  • 31
    • 18444406959 scopus 로고    scopus 로고
    • A. J. Berglund, Dartmouth College B. A. thesis, 2000, also in e-print quant-ph/0010001
    • A. J. Berglund, Dartmouth College B. A. thesis, 2000, also in e-print quant-ph/0010001.
  • 32
    • 18444369729 scopus 로고    scopus 로고
    • note
    • s= ω. Hence, the only independent variable to integrate over is the deviation ε from half of the pump frequency (for either idler or signal photon).
  • 34
  • 35
    • 51349163744 scopus 로고
    • whereas F(ρ,σ) ≡ Tr√√ρσ√ρ is the definition in Ref. [1]
    • 2 is the definition given by R. Jozsa, J. Mod. Opt. 41, 2315 (1994), whereas F(ρ,σ) ≡ Tr√√ρσ√ρ is the definition in Ref. [1].
    • (1994) J. Mod. Opt. , vol.41 , pp. 2315
    • Jozsa, R.1
  • 38
    • 18444398445 scopus 로고    scopus 로고
    • J. B. Altepeter et al. (unpublished)
    • J. B. Altepeter et al. (unpublished).
  • 39
    • 18444368231 scopus 로고    scopus 로고
    • note
    • If p≤ 1/2, we may need to attenuate the intensity of the photon pair from the first set of crystals. Alternatively, to losslessly prepare the state, we can switch the order of the setup such that the pure state |ψ〉 is created in the first set of crystals, and the mixed state σ is created in the second. However, the photons from the former will then have to be precompensated to eliminate the effect of the subsequent decoherence. This can be done by using the same decoherers but with their optic axes rotated by 90°.
  • 41
    • 18444386308 scopus 로고    scopus 로고
    • note
    • If the pump is decohered before the second set of crystals, the down-conversion pair will be in a mixed state (up to local uni taries) (0 0 0 0 0 λ g√λ(1-λ) 0 0 g* √ λ(1-λ) 1-λ 0 0 0 0 0) where g represents the degree of decoherence of the pump [cf., f in Eq. (14)]. It is not clear whether this additional "knob" boosts the number of independent controlled parameters from 12 to 13.
  • 47
    • 18444370360 scopus 로고    scopus 로고
    • A. G. White et al., e-print quant-ph/0308115
    • A. G. White et al., e-print quant-ph/0308115.


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.