sptwoquditop.m

该算法是用于量子运算的matlab程序

% sptwoquditop   Operator on given qudits; sparse version
%   sptwoquditop(op,k1,k2,n) defines an n-qudit quantum operator
%   which corresponds to operator op acting on the k1th and k2th qudits.
%   Qubit position is interpreted as with reorder.
%   The dimension of the qudit is deduced from the size of op.
%   If n is omitted, then its value is taken to be the value of global
%   variable N. 

% Copyright (C) 2005  Geza Toth    E.mail: [e-mail]
%
% This program is free software; you can redistribute it and/or
% modify it under the terms of the GNU General Public License
% as published by the Free Software Foundation; see gpl.txt
% of this subroutine package.
%
% This program is distributed in the hope that it will be useful,
% but WITHOUT ANY WARRANTY; without even the implied warranty of
% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
% GNU General Public License for more details.
% 
% You should have received a copy of the GNU General Public License
% along with this program; if not, write to the Free Software
% Foundation, Inc., 51 Franklin Street, Fifth Floor, 
% Boston, MA  02110-1301, USA.

function mop=sptwoquditop(op,k1,k2,varargin)
if isempty(varargin),
    global N;
else
    if length(varargin)~=1,
        error('Wrong number of input arguments.')
    end %if
    N=varargin{1};
end %if

kk1=min(k1,k2);
kk2=max(k1,k2);

[sy,sx]=size(op);
d=sqrt(sx);

mop=kron(speye(d^(N-kk1-1)),op);
mop=kron(mop,speye(d^(kk1-1)));
mop=swapqudits(mop,kk2,kk1+1);