Is there any current and/or upcoming technology that alerts Air Traffic Controllers in case of loss of aircraft separation?
Most air traffic control systems nowaday have various safety net functions built into them. Short Term Conflict Alerting is one of these functions.

Short Term Conflict Alerting (STCA) works on the basis of extrapolating the current position using velocity and turn rate to predict imminent separation violations. If such a imminent separation violation is detected, the system will alert the air traffic controller. 

The next level of conflict alering is Medium Term Conflict Detection (MTCD); this is not considered a safety net, but a tool that assists the Controller in detecting conflicts early on (up to 20 minutes in advance). Instead of relying on simple position extrapolation, MTCD uses more advance trajectory predictions that combine knowledge of the current aircraft position and velocity with information from aircraft performance models, flight plan, weather and given ATC instructions. 
MTCD development started 20 years ago, and the tool is now being implemented in various ATC systems.