Baker, who was at the end of a rehab stint for a right hand sprain, said he learned of the trade in a conversation with Cubs general manager Jim Hendry on Wednesday night.
"I haven't talked with [Cubs manager] Lou Piniella, but I did talk with Jim Hendry last night," said Baker as he headed to a flight Thursday morning so he could join the Cubs for their game against the Brewers at Wrigley Field on Thursday night. "I'm excited for the opportunity. I don't know what their plans are for me yet, so I'm looking forward to getting there."
Baker was hitting .130 with three RBIs for the Rockies in limited playing time before the injury forced him to the disabled list on April 27. In seven injury rehab games at Triple-A Colorado Springs, Baker hit .217 with a home run, two doubles and 10 RBIs.
Baker hit .257 with 22 home runs and 88 RBIs in 231 games with the Rockies from 2005-09.
To make room on their roster, the Cubs designated infielder Ryan Freel for assignment.
The Rockies selected Baker in the fourth round in the 2000 First-Year Player Draft after an outstanding college career at Clemson. A third baseman by trade, Baker was blocked by Garrett Atkins and expanded to play second base, the outfield and first base in order to receive playing time, but never received it on a consistent basis.
The Rockies' roster remains crowded at his positions.
"We had to make a timing decision because we were at the end of Jeff's rehab period," O'Dowd said. "There really wasn't a spot for Jeff on our club. I told him that if we didn't have a specific opening, we'd look to move him. That's exactly what took place."
Alburquerque, 23, was 1-0 with a 2.08 ERA in 24 relief appearances at Daytona, with 44 strikeouts to 14 walks.
"He's got a very good arm and a chance to move very quickly," O'Dowd said.
Thomas Harding is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.