You can simplify the code a little:

#! perl -sw
use 5.010;
use strict;
use Data::Dump qw[ pp ];

my $abstract = 'Perl is a high-level, general-purpose, interpreted, dy
+namic programming language.';

my (%double_words, %triple_words, %four_words);

my @words = split ' ', $abstract;

$double_words{ join ' ', @words[ $_ .. $_ +1 ] } = undef for 0 .. $#wo
+rds - 1;
$triple_words{ join ' ', @words[ $_ .. $_ +2 ] } = undef for 0 .. $#wo
+rds - 2;
$four_words{   join ' ', @words[ $_ .. $_ +3 ] } = undef for 0 .. $#wo
+rds - 3;

say join '|', keys %double_words;
say join '|', keys %triple_words;
say join '|', keys %four_words;
[download]

But that's doing essentially the same amount of work. I don't see much in the way of optimisations, but do you need them? How big can your abstracts get?

I ran the above on a text contain 21,000 words and it took a little over 1/10th second.