Lasers for Quantum Photonics

Author: the photonics expert Dr. Rüdiger Paschotta

Various types of lasers are needed for specific purposes in quantum photonics. Often they have to meet quite special requirements. Some examples are given in the following sections.

Application Areas

Lasers as Pump Sources for Single-photon or Photon Pair Emitters

Single-photon emitters, as needed e.g. in quantum communications, are generally no lasers (even when containing a light emitter in an optical resonator). However, some of them (e.g. based on quantum dots) require a pulsed laser (e.g. a picosecond laser) as a pump source. Such a laser must provide a short light pulse with low pulse energy, preferably with a reasonable efficiency, i.e., with very low power consumption, and high beam quality. Often it also needs to emit in a special wavelength range. Laser diodes are frequently used.

For the generation of entangled photon pairs in nonlinear crystal materials, one also requires a pump laser. The demands can be very different depending on the concrete case, for example concerning pulsed or continuous-wave operation, optical power or pulse energy, emission wavelength, etc. Frequently, a short emission wavelength, a narrow linewidth and a high beam quality are required.

Lasers for Manipulating and Readout of Quantum Bits

Quantum bits (qbits) are often manipulated (e.g. initialized) and/or read with laser pulses. Essential requirements for the laser are usually a special emission wavelength and a small linewidth, as well as precise control of the timing and energy of the pulses.

Lasers for Trapping and Cooling of Atoms and Ions

Lasers are used for optical traps, capturing multiple atoms or ions, or sometimes a single atom or ion. Such atoms or ions can be used to represent quantum states. This often requires continuous wave operation of the laser(s) at a specific wavelength and with a low linewidth. Depending on the circumstances, the required optical power can be considerable.

Spectroscopy in Quantum Sensing and Metrology

Ultra-stable lasers with very low laser noise, a narrow linewidth, and possibly some wavelength tuning are used for precision spectroscopy in quantum sensing devices, where photon entanglement, single photons, or squeezed states of light are used for extremely precise measurements.

In some cases, a frequency comb from a accurately stabilized mode-locked laser is required instead of a single-frequency output. There are several powerful methods of frequency comb spectroscopy.

Indirect Uses

Lasers can also find various indirect uses for quantum photonics, e.g. for the fabrication of photonic integrated circuits by ultrashort pulse laser material processing

Typical Requirements

Some typical requirements for such lasers, as already mentioned above, are:

• special emission wavelengths, which are often not accessible by common laser gain media
• narrow linewidth
• very low laser noise and high beam quality

More to Learn

Encyclopedia articles:

• quantum photonics