Photon Factory Activity Report 2004 #22 Part B (2005)
Atomic and Molecular Science

20A/2003G173

Quantum phase control using pulsed Stark electric field
Isao Sakakida, Tomohiro Aoto*, Yumio Morioka
Institute of Physics, University of Tsukuba, Tsukuba City, Ibaraki 305-8571, Japanproportional to field strength in this state) and detect it.

1800

ns(3/2)1nd(3/2)11600 nd(1/2)1
1400

18d(3/2)

ns'(1/2)1nd'(3/2)1788.5

789.0

1200

countsIntroduction
Interest for quantum computing and quantum information
has been growing, owing quantum superposition andentanglement since D. Deutsch has proposed quantum
computing [1]. For the aim of quantum computation realization,some physical systems for quantum computation such as NMR,
quantum dots and photons have been proposed and studied[2].
However, there are many problems such as limitation ofcoherence time, the qubits extensibility and so on. In order toovercome these problems, techniques of controlling anddetecting quantum state become increasingly important.
Quantum interference control using Stark effect of atom has
been performed by Ryabtsev et al [3]. In their study, probabilityof mixing between the Rydberg states depends on not only
initial probability distribution but also phase difference between
degenerate states.
We investigate the quantum state control possibilities using
Rydberg atom detecting Stark quantum beat (SQB) fromexcited Rydberg state.

1000
800
600
400
2000
787.0

787.5

788.0

789.5

790.0

wavelength [Å]Fig1 Ar fluorescence spectrum

Results and Discussion
Fig.1 shows an fluorescence excitation spectrum of Ar below
the first ionization theshold. The 18d[3/2] state, which strongly
appears in Fig.1, has been investigated well about fielddependence of the beats[4]. The SQB of this state can beobserved with less than 1V/cm. Flourescence intensity fromsuperposition state caused by Stark effect is expressed asfollows.

Where θ is angle between plane of polarization and electricfeild direction. If we cease impressing external field, timedependent wave function of the Rydberg state get a phasechange. Consequently the effect of phase difference appear inflourescence intensity after the pulsed electric field(Fig. 2).
Therefore, we can control quantum state by duration time tp,
angle θ and energy splitting width E1-E2(which is500

Fluorescence intensity [arb. unit]

Experiment
The SQB measurement was performed by using PF ring
single bunch operation. We used Stark plates applied an electricfield to the interaction region. The direction of linearlypolarized light was set to +45˚ with respect to the external
electric field direction. This setting makes it possible to excite
the superposition state of M=0 and |M| =1 magnetic sublevels.
The phase differences between two energy levels could bemeasured and controlled by applying a pulsed electric field.

∆=πpulsed electric field

0500∆=3/2π0500∆=2π0500∆=4π00200time [nsec]

400

Fig.2 Time dependence of fluorescence intensity[1] D. Deutsch, Proc. R. Soc. London A 400, 97 (1985).
[2] I. L. Chuang et al, Phys. Rev. Lett, 85, 005452 (2000)[3] I. I. Ryabtsev et al. Phys. Rev. A 61, 063414 (2000).
[4] T. Aoto et al, J. Ele. Spectros. 144, 47-50 (2005)*tomohiro.aoto@kek.jp

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