Writing the notation when gates act on non successive registers





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Suppose I have registers $|arangle^{l}|brangle^{l} |crangle^{l}$ and want an adder mod $l$ gate between the $a$ and $c$ registers. Let $R$ be the adder mod $l$ gate. So is this the correct notation for an operator $U$ that implements this $$ U=Rotimes I_b^{otimes l}.$$ But how do I convey that $R$ is between $a$ and $c$ and $I$ is for the register $b$?










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    $begingroup$


    Suppose I have registers $|arangle^{l}|brangle^{l} |crangle^{l}$ and want an adder mod $l$ gate between the $a$ and $c$ registers. Let $R$ be the adder mod $l$ gate. So is this the correct notation for an operator $U$ that implements this $$ U=Rotimes I_b^{otimes l}.$$ But how do I convey that $R$ is between $a$ and $c$ and $I$ is for the register $b$?










    share|improve this question











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      3












      3








      3





      $begingroup$


      Suppose I have registers $|arangle^{l}|brangle^{l} |crangle^{l}$ and want an adder mod $l$ gate between the $a$ and $c$ registers. Let $R$ be the adder mod $l$ gate. So is this the correct notation for an operator $U$ that implements this $$ U=Rotimes I_b^{otimes l}.$$ But how do I convey that $R$ is between $a$ and $c$ and $I$ is for the register $b$?










      share|improve this question











      $endgroup$




      Suppose I have registers $|arangle^{l}|brangle^{l} |crangle^{l}$ and want an adder mod $l$ gate between the $a$ and $c$ registers. Let $R$ be the adder mod $l$ gate. So is this the correct notation for an operator $U$ that implements this $$ U=Rotimes I_b^{otimes l}.$$ But how do I convey that $R$ is between $a$ and $c$ and $I$ is for the register $b$?







      quantum-gate quantum-state notation tensor-product






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      edited May 28 at 14:10









      Sanchayan Dutta

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      asked May 28 at 10:11









      UpstartUpstart

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          $begingroup$

          Personally, I would just define $R_{ac}$ to be the unitary that acts $R$ between registers $a$ and $c$, and acts as identity everywhere else.






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            2
















            $begingroup$

            As always with notation there is not a "correct" way of doing things: it's just arbitrary conventions.



            The most readable notation I see for your example involves separating the unitary $R$ into 2 virtual unitary matrices:





            • $R_a$ the portion that acts on $vert a rangle^l$.


            • $R_c$ the portion that acts on $vert c rangle^l$.


            and "defining" $R$ as
            $$
            R = R_a otimes R_c.
            $$




            I called the matrices $R_a$ and $R_c$ "virtual unitaries because it is likely that they do not exist: the decomposition $R = R_a otimes R_c$ will probably be impossible to compute because the matrix $R$ cannot be split as 2 separate transformations on $vert a rangle^l$ and $vert c rangle^l$.




            Warning with this kind of non-standard notation: as the matrices involved are not really matrices (they are introduced just for the notation and might not exist), it may add more complexity/confusion than it helps.



            In the end, your operation on $vert a rangle^lvert b rangle^lvert c rangle^l$ may be written as
            $$
            U = R_a otimes I otimes R_c.
            $$






            share|improve this answer












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              $begingroup$

              Personally, I would just define $R_{ac}$ to be the unitary that acts $R$ between registers $a$ and $c$, and acts as identity everywhere else.






              share|improve this answer










              $endgroup$




















                3
















                $begingroup$

                Personally, I would just define $R_{ac}$ to be the unitary that acts $R$ between registers $a$ and $c$, and acts as identity everywhere else.






                share|improve this answer










                $endgroup$


















                  3














                  3










                  3







                  $begingroup$

                  Personally, I would just define $R_{ac}$ to be the unitary that acts $R$ between registers $a$ and $c$, and acts as identity everywhere else.






                  share|improve this answer










                  $endgroup$



                  Personally, I would just define $R_{ac}$ to be the unitary that acts $R$ between registers $a$ and $c$, and acts as identity everywhere else.







                  share|improve this answer













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                  answered May 28 at 15:52









                  DaftWullieDaftWullie

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                      2
















                      $begingroup$

                      As always with notation there is not a "correct" way of doing things: it's just arbitrary conventions.



                      The most readable notation I see for your example involves separating the unitary $R$ into 2 virtual unitary matrices:





                      • $R_a$ the portion that acts on $vert a rangle^l$.


                      • $R_c$ the portion that acts on $vert c rangle^l$.


                      and "defining" $R$ as
                      $$
                      R = R_a otimes R_c.
                      $$




                      I called the matrices $R_a$ and $R_c$ "virtual unitaries because it is likely that they do not exist: the decomposition $R = R_a otimes R_c$ will probably be impossible to compute because the matrix $R$ cannot be split as 2 separate transformations on $vert a rangle^l$ and $vert c rangle^l$.




                      Warning with this kind of non-standard notation: as the matrices involved are not really matrices (they are introduced just for the notation and might not exist), it may add more complexity/confusion than it helps.



                      In the end, your operation on $vert a rangle^lvert b rangle^lvert c rangle^l$ may be written as
                      $$
                      U = R_a otimes I otimes R_c.
                      $$






                      share|improve this answer












                      $endgroup$




















                        2
















                        $begingroup$

                        As always with notation there is not a "correct" way of doing things: it's just arbitrary conventions.



                        The most readable notation I see for your example involves separating the unitary $R$ into 2 virtual unitary matrices:





                        • $R_a$ the portion that acts on $vert a rangle^l$.


                        • $R_c$ the portion that acts on $vert c rangle^l$.


                        and "defining" $R$ as
                        $$
                        R = R_a otimes R_c.
                        $$




                        I called the matrices $R_a$ and $R_c$ "virtual unitaries because it is likely that they do not exist: the decomposition $R = R_a otimes R_c$ will probably be impossible to compute because the matrix $R$ cannot be split as 2 separate transformations on $vert a rangle^l$ and $vert c rangle^l$.




                        Warning with this kind of non-standard notation: as the matrices involved are not really matrices (they are introduced just for the notation and might not exist), it may add more complexity/confusion than it helps.



                        In the end, your operation on $vert a rangle^lvert b rangle^lvert c rangle^l$ may be written as
                        $$
                        U = R_a otimes I otimes R_c.
                        $$






                        share|improve this answer












                        $endgroup$


















                          2














                          2










                          2







                          $begingroup$

                          As always with notation there is not a "correct" way of doing things: it's just arbitrary conventions.



                          The most readable notation I see for your example involves separating the unitary $R$ into 2 virtual unitary matrices:





                          • $R_a$ the portion that acts on $vert a rangle^l$.


                          • $R_c$ the portion that acts on $vert c rangle^l$.


                          and "defining" $R$ as
                          $$
                          R = R_a otimes R_c.
                          $$




                          I called the matrices $R_a$ and $R_c$ "virtual unitaries because it is likely that they do not exist: the decomposition $R = R_a otimes R_c$ will probably be impossible to compute because the matrix $R$ cannot be split as 2 separate transformations on $vert a rangle^l$ and $vert c rangle^l$.




                          Warning with this kind of non-standard notation: as the matrices involved are not really matrices (they are introduced just for the notation and might not exist), it may add more complexity/confusion than it helps.



                          In the end, your operation on $vert a rangle^lvert b rangle^lvert c rangle^l$ may be written as
                          $$
                          U = R_a otimes I otimes R_c.
                          $$






                          share|improve this answer












                          $endgroup$



                          As always with notation there is not a "correct" way of doing things: it's just arbitrary conventions.



                          The most readable notation I see for your example involves separating the unitary $R$ into 2 virtual unitary matrices:





                          • $R_a$ the portion that acts on $vert a rangle^l$.


                          • $R_c$ the portion that acts on $vert c rangle^l$.


                          and "defining" $R$ as
                          $$
                          R = R_a otimes R_c.
                          $$




                          I called the matrices $R_a$ and $R_c$ "virtual unitaries because it is likely that they do not exist: the decomposition $R = R_a otimes R_c$ will probably be impossible to compute because the matrix $R$ cannot be split as 2 separate transformations on $vert a rangle^l$ and $vert c rangle^l$.




                          Warning with this kind of non-standard notation: as the matrices involved are not really matrices (they are introduced just for the notation and might not exist), it may add more complexity/confusion than it helps.



                          In the end, your operation on $vert a rangle^lvert b rangle^lvert c rangle^l$ may be written as
                          $$
                          U = R_a otimes I otimes R_c.
                          $$







                          share|improve this answer















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                          edited May 28 at 17:36

























                          answered May 28 at 11:48









                          NelimeeNelimee

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