2
3 B S c i e n t i f i c ® E x p e r i m e n t s
. . . g o i n g o n e s t e p f u r t h e r
M1
BS1
2
1
P
(45°)
M2
BS2
LASER
2
1
A
(45°)
LASER
2
1
P1
P2
(0°)
(90°)
LASER
Mach-Zehnder interferoMeter
OP T IC S /
WAV E OP T IC S
OBJECTIVE
Demonstration of “quantum erasure” in an experiment by analogy.
Ue4030520
BASIC PRINCIPL ES
Light itself can be described in quantum mechanics by means of wave equations. From this it is
possible to derive the spatial distribution of the probability density in the form of the square of
the modulus of the wave function. The combination of two beams corresponds to superposition
of two wave functions. The probability density then contains a mixed term which describes the
interference pattern. Light is therefore suitable for experiments which demonstrate quantum
mechanical phenomena by analogy.
Ue4030520
SUMM A RY
Light itself can be described in quantum mechanics by means of wave equations. From this it is pos-
sible to derive the spatial distribution of the probability density in the form of the square of the
modulus of the wave function. Light is therefore suitable for experiments which demonstrate quantum
mechanical phenomena by analogy. Such an analogy experiment demonstrates the so-called quantum
eraser effect by setting up a Mach-Zehnder interferometer and observing interference between the
split beams on a screen. If two perpendicular polarisers are placed in the paths of the split beams, the
interference vanishes since, in quantum mechanical terms, it is possible to determine the path a pho-
ton has taken. If a third polarising filter set at an angle of 45° is placed directly in front of the screen,
this quantum information is “erased” and the interference can be seen once again.
E X PERIMEN T
PROCEDURE
