A temporally continuous matter wave beam splitter (14) comprising a plurality of intersecting and interfering laser beam (kr, kb), which act as waveguides for a matter wave beam. The laser beams of the waveguides each have a frequency detuned below a frequency of an internal atomic transition of the matter wave. The matter wave has a wavevector which is an integral multiple of the wavevector of the laser beams within a region of intersection of the laser beams. There is also provided an atomic interferometer (200) comprising such a continuous matter wave beam splitter, and a solid state device comprising such a continuous matter wave beam splitter, which may be part of an atomic interferometer. A cold atom gyroscope, a cold atom accelerometer or a cold atom gravimeter comprising such a solid state device are also provided. There is further provided a quantum computer comprising such a solid state device, wherein atoms of the matter wave beam are in an entangled quantum state. There is also provided a method of splitting a matter wave beam, comprising introducing the matter wave beam into a first temporally continuous laser beam, the frequency of which is detuned below a frequency of an internal atomic transition of the matter wave beam; intersecting and interfering the first continuous laser beam with a second temporally continuous laser beam, the frequency of which is also detuned below the frequency of the internal atomic transition of the matter wave beam; providing the matter wave beam with a wavevector which is an integral multiple of the wavevector of the first and second laser beams within a region of intersection of the laser beams, whereby the laser beams act as waveguides for the matter wave beam.