Is the photon pair generated from the electron-positron annihilation entangled?











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Is the photon pair generated from the electron-positron annihilation entangled?



And would they work as a source of entangled photons suitable for experiments in quantum optics?






quantum-mechanics particle-physics photons quantum-entanglement







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    up vote
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    Is the photon pair generated from the electron-positron annihilation entangled?



    And would they work as a source of entangled photons suitable for experiments in quantum optics?






    quantum-mechanics particle-physics photons quantum-entanglement







    share|cite|improve this question


























      up vote
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      favorite
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      up vote
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      down vote

      favorite
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      Is the photon pair generated from the electron-positron annihilation entangled?



      And would they work as a source of entangled photons suitable for experiments in quantum optics?






      quantum-mechanics particle-physics photons quantum-entanglement







      share|cite|improve this question















      Is the photon pair generated from the electron-positron annihilation entangled?



      And would they work as a source of entangled photons suitable for experiments in quantum optics?






      quantum-mechanics particle-physics photons quantum-entanglement




      quantum-mechanics particle-physics photons quantum-entanglement






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      share|cite|improve this question













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      edited yesterday









      Peter Mortensen

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      asked yesterday









      E.phy

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      1807






















          2 Answers
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          Yes, they are definitely entangled. Their combined energy will exactly equal the combined energy of the original electron-positron pair, for example. The same is true for combined momentum and combined spin.






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          • "Combined spin" should also include any orbital angular momentum if the electron and positron briefly orbited each other (positronium) before annihilating.
            – Andreas Blass
            yesterday










          • That is correct--
            – S. McGrew
            yesterday










          • And from what I understand about these things (only a layman as far as physics goes), the angular momentum of the electron-positron pair will almost always be non-zero.
            – EvilSnack
            23 hours ago


















          up vote
          2
          down vote













          The photon-pair is definitely entangled. It is produced from an $S$-wave state of the electron-positron system and as such has orbital angular momentum $L=0$. But it's not useful for quantum optics, the photons' energy is too high for your usual mirrors to reflect. See fig 33.15 on p. 23 of this http://pdg.lbl.gov/2018/reviews/rpp2018-rev-passage-particles-matter.pdf to get an idea what happens to a 511 keV photon from two-photon annihilation of an electron-positron pair at rest once it hits matter: ionization by Compton scattering dominates the interaction, that's not what you want to happen in a mirror or lense.



          It's worth keeping in mind though, that the electron-positron system (Positronium) can decay to any number of photons $>1$, though numbers higher than three are very rare. An even number of photons can be produced for decays of the singlet ground state ${}^1S_0$ (where the electron and positron are in an anti-symmetric spin state
          $frac{1}{sqrt{2}}left( left|uparrow downarrow rightrangle - left|downarrow uparrow rightrangleright)$, "Parapositronium"). This defines the spin entanglement in the case you had in mind, and it has actually been measured and found to agree with full entanglement, see e.g. here http://adsabs.harvard.edu/abs/2009APS..HAW.GB108S



          An uneven number can be produced from the triplet ${}^3S_0$ ("Orthopositronium"). The triplet is much longer-lived than the singlet state (roughly thousand times), but since it consists of three states and because symmetries ($CP$) prevent the positronium from going from the triplet to the singlet state, an appreciable number of electron-positron pairs decays to three photons.



          In fact, also the $S$ states of higher energy levels can decay to photons directly, but usually they will decay to the ground state first, emitting photons of energies $O(10 - 100 emathrm{V})$ before the actual decay to the high-energy pair or to the three continuous spectrum photons.






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            2 Answers
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            active

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            2 Answers
            2






            active

            oldest

            votes









            active

            oldest

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            active

            oldest

            votes








            up vote
            21
            down vote













            Yes, they are definitely entangled. Their combined energy will exactly equal the combined energy of the original electron-positron pair, for example. The same is true for combined momentum and combined spin.






            share|cite|improve this answer





















            • "Combined spin" should also include any orbital angular momentum if the electron and positron briefly orbited each other (positronium) before annihilating.
              – Andreas Blass
              yesterday










            • That is correct--
              – S. McGrew
              yesterday










            • And from what I understand about these things (only a layman as far as physics goes), the angular momentum of the electron-positron pair will almost always be non-zero.
              – EvilSnack
              23 hours ago















            up vote
            21
            down vote













            Yes, they are definitely entangled. Their combined energy will exactly equal the combined energy of the original electron-positron pair, for example. The same is true for combined momentum and combined spin.






            share|cite|improve this answer





















            • "Combined spin" should also include any orbital angular momentum if the electron and positron briefly orbited each other (positronium) before annihilating.
              – Andreas Blass
              yesterday










            • That is correct--
              – S. McGrew
              yesterday










            • And from what I understand about these things (only a layman as far as physics goes), the angular momentum of the electron-positron pair will almost always be non-zero.
              – EvilSnack
              23 hours ago













            up vote
            21
            down vote










            up vote
            21
            down vote









            Yes, they are definitely entangled. Their combined energy will exactly equal the combined energy of the original electron-positron pair, for example. The same is true for combined momentum and combined spin.






            share|cite|improve this answer












            Yes, they are definitely entangled. Their combined energy will exactly equal the combined energy of the original electron-positron pair, for example. The same is true for combined momentum and combined spin.







            share|cite|improve this answer












            share|cite|improve this answer



            share|cite|improve this answer










            answered yesterday









            S. McGrew

            5,2452923




            5,2452923












            • "Combined spin" should also include any orbital angular momentum if the electron and positron briefly orbited each other (positronium) before annihilating.
              – Andreas Blass
              yesterday










            • That is correct--
              – S. McGrew
              yesterday










            • And from what I understand about these things (only a layman as far as physics goes), the angular momentum of the electron-positron pair will almost always be non-zero.
              – EvilSnack
              23 hours ago


















            • "Combined spin" should also include any orbital angular momentum if the electron and positron briefly orbited each other (positronium) before annihilating.
              – Andreas Blass
              yesterday










            • That is correct--
              – S. McGrew
              yesterday










            • And from what I understand about these things (only a layman as far as physics goes), the angular momentum of the electron-positron pair will almost always be non-zero.
              – EvilSnack
              23 hours ago
















            "Combined spin" should also include any orbital angular momentum if the electron and positron briefly orbited each other (positronium) before annihilating.
            – Andreas Blass
            yesterday




            "Combined spin" should also include any orbital angular momentum if the electron and positron briefly orbited each other (positronium) before annihilating.
            – Andreas Blass
            yesterday












            That is correct--
            – S. McGrew
            yesterday




            That is correct--
            – S. McGrew
            yesterday












            And from what I understand about these things (only a layman as far as physics goes), the angular momentum of the electron-positron pair will almost always be non-zero.
            – EvilSnack
            23 hours ago




            And from what I understand about these things (only a layman as far as physics goes), the angular momentum of the electron-positron pair will almost always be non-zero.
            – EvilSnack
            23 hours ago










            up vote
            2
            down vote













            The photon-pair is definitely entangled. It is produced from an $S$-wave state of the electron-positron system and as such has orbital angular momentum $L=0$. But it's not useful for quantum optics, the photons' energy is too high for your usual mirrors to reflect. See fig 33.15 on p. 23 of this http://pdg.lbl.gov/2018/reviews/rpp2018-rev-passage-particles-matter.pdf to get an idea what happens to a 511 keV photon from two-photon annihilation of an electron-positron pair at rest once it hits matter: ionization by Compton scattering dominates the interaction, that's not what you want to happen in a mirror or lense.



            It's worth keeping in mind though, that the electron-positron system (Positronium) can decay to any number of photons $>1$, though numbers higher than three are very rare. An even number of photons can be produced for decays of the singlet ground state ${}^1S_0$ (where the electron and positron are in an anti-symmetric spin state
            $frac{1}{sqrt{2}}left( left|uparrow downarrow rightrangle - left|downarrow uparrow rightrangleright)$, "Parapositronium"). This defines the spin entanglement in the case you had in mind, and it has actually been measured and found to agree with full entanglement, see e.g. here http://adsabs.harvard.edu/abs/2009APS..HAW.GB108S



            An uneven number can be produced from the triplet ${}^3S_0$ ("Orthopositronium"). The triplet is much longer-lived than the singlet state (roughly thousand times), but since it consists of three states and because symmetries ($CP$) prevent the positronium from going from the triplet to the singlet state, an appreciable number of electron-positron pairs decays to three photons.



            In fact, also the $S$ states of higher energy levels can decay to photons directly, but usually they will decay to the ground state first, emitting photons of energies $O(10 - 100 emathrm{V})$ before the actual decay to the high-energy pair or to the three continuous spectrum photons.






            share|cite|improve this answer



























              up vote
              2
              down vote













              The photon-pair is definitely entangled. It is produced from an $S$-wave state of the electron-positron system and as such has orbital angular momentum $L=0$. But it's not useful for quantum optics, the photons' energy is too high for your usual mirrors to reflect. See fig 33.15 on p. 23 of this http://pdg.lbl.gov/2018/reviews/rpp2018-rev-passage-particles-matter.pdf to get an idea what happens to a 511 keV photon from two-photon annihilation of an electron-positron pair at rest once it hits matter: ionization by Compton scattering dominates the interaction, that's not what you want to happen in a mirror or lense.



              It's worth keeping in mind though, that the electron-positron system (Positronium) can decay to any number of photons $>1$, though numbers higher than three are very rare. An even number of photons can be produced for decays of the singlet ground state ${}^1S_0$ (where the electron and positron are in an anti-symmetric spin state
              $frac{1}{sqrt{2}}left( left|uparrow downarrow rightrangle - left|downarrow uparrow rightrangleright)$, "Parapositronium"). This defines the spin entanglement in the case you had in mind, and it has actually been measured and found to agree with full entanglement, see e.g. here http://adsabs.harvard.edu/abs/2009APS..HAW.GB108S



              An uneven number can be produced from the triplet ${}^3S_0$ ("Orthopositronium"). The triplet is much longer-lived than the singlet state (roughly thousand times), but since it consists of three states and because symmetries ($CP$) prevent the positronium from going from the triplet to the singlet state, an appreciable number of electron-positron pairs decays to three photons.



              In fact, also the $S$ states of higher energy levels can decay to photons directly, but usually they will decay to the ground state first, emitting photons of energies $O(10 - 100 emathrm{V})$ before the actual decay to the high-energy pair or to the three continuous spectrum photons.






              share|cite|improve this answer

























                up vote
                2
                down vote










                up vote
                2
                down vote









                The photon-pair is definitely entangled. It is produced from an $S$-wave state of the electron-positron system and as such has orbital angular momentum $L=0$. But it's not useful for quantum optics, the photons' energy is too high for your usual mirrors to reflect. See fig 33.15 on p. 23 of this http://pdg.lbl.gov/2018/reviews/rpp2018-rev-passage-particles-matter.pdf to get an idea what happens to a 511 keV photon from two-photon annihilation of an electron-positron pair at rest once it hits matter: ionization by Compton scattering dominates the interaction, that's not what you want to happen in a mirror or lense.



                It's worth keeping in mind though, that the electron-positron system (Positronium) can decay to any number of photons $>1$, though numbers higher than three are very rare. An even number of photons can be produced for decays of the singlet ground state ${}^1S_0$ (where the electron and positron are in an anti-symmetric spin state
                $frac{1}{sqrt{2}}left( left|uparrow downarrow rightrangle - left|downarrow uparrow rightrangleright)$, "Parapositronium"). This defines the spin entanglement in the case you had in mind, and it has actually been measured and found to agree with full entanglement, see e.g. here http://adsabs.harvard.edu/abs/2009APS..HAW.GB108S



                An uneven number can be produced from the triplet ${}^3S_0$ ("Orthopositronium"). The triplet is much longer-lived than the singlet state (roughly thousand times), but since it consists of three states and because symmetries ($CP$) prevent the positronium from going from the triplet to the singlet state, an appreciable number of electron-positron pairs decays to three photons.



                In fact, also the $S$ states of higher energy levels can decay to photons directly, but usually they will decay to the ground state first, emitting photons of energies $O(10 - 100 emathrm{V})$ before the actual decay to the high-energy pair or to the three continuous spectrum photons.






                share|cite|improve this answer














                The photon-pair is definitely entangled. It is produced from an $S$-wave state of the electron-positron system and as such has orbital angular momentum $L=0$. But it's not useful for quantum optics, the photons' energy is too high for your usual mirrors to reflect. See fig 33.15 on p. 23 of this http://pdg.lbl.gov/2018/reviews/rpp2018-rev-passage-particles-matter.pdf to get an idea what happens to a 511 keV photon from two-photon annihilation of an electron-positron pair at rest once it hits matter: ionization by Compton scattering dominates the interaction, that's not what you want to happen in a mirror or lense.



                It's worth keeping in mind though, that the electron-positron system (Positronium) can decay to any number of photons $>1$, though numbers higher than three are very rare. An even number of photons can be produced for decays of the singlet ground state ${}^1S_0$ (where the electron and positron are in an anti-symmetric spin state
                $frac{1}{sqrt{2}}left( left|uparrow downarrow rightrangle - left|downarrow uparrow rightrangleright)$, "Parapositronium"). This defines the spin entanglement in the case you had in mind, and it has actually been measured and found to agree with full entanglement, see e.g. here http://adsabs.harvard.edu/abs/2009APS..HAW.GB108S



                An uneven number can be produced from the triplet ${}^3S_0$ ("Orthopositronium"). The triplet is much longer-lived than the singlet state (roughly thousand times), but since it consists of three states and because symmetries ($CP$) prevent the positronium from going from the triplet to the singlet state, an appreciable number of electron-positron pairs decays to three photons.



                In fact, also the $S$ states of higher energy levels can decay to photons directly, but usually they will decay to the ground state first, emitting photons of energies $O(10 - 100 emathrm{V})$ before the actual decay to the high-energy pair or to the three continuous spectrum photons.







                share|cite|improve this answer














                share|cite|improve this answer



                share|cite|improve this answer








                edited 15 hours ago

























                answered 17 hours ago









                tobi_s

                1612




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