Quantum machine

The quantum machine is a machine that can be described by quantum mechanics, their movements, while their description in the framework of classical mechanics is not possible. The first quantum machine was developed under the direction of Andrew N. Cleland and John M. Martinis in 2009 by Aaron D. O'Connell at the University of California, Santa Barbara as part of its promotion. This machine consists of a quantum 40 great mechanical oscillator, which is electrically coupled to a qubit. In the experiments was different quantum phenomena such as the controlled generation of quantized vibrational states ( phonons) and the quantum entanglement of these vibrational states are observed with the qubit. The U.S. journal Science, the quantum machine for scientific breakthrough of the year ( English: " breakthrough of the year" ) awarded 2010.

Background

The idea that not only objects in the order of molecules, but also macroscopic objects could follow the laws of quantum mechanics, has been available since the early days of quantum mechanics in the early 20th century. In the order of molecules and including experimental measurements already delivered results that contradict classical physics. However, quantum effects in macroscopic objects are not easily observable. The energy quantum macroscopic objects are so small that energy changes seem to occur continuously. Furthermore, very efficiently suppressed by unavoidable decoherence effects in the typical microscopic systems interference effects. When developed by O'Connell quantum machine these problems could be solved by an optimized resonator design and various other design measures partially.

Structure of the quantum machine O'Connellschen

The oscillator developed by O'Connell quantum machine was a product manufactured in thin-film technology piezoelectric element made ​​of aluminum nitride having a diameter of 40 and a thickness of 330 nm, which diameter corresponds to the diameter of thin human fluff hair, the oscillation of the quantum machine was barely visible to the naked eye. By applying an alternating electric voltage between the electrodes expansion vibrations of the piezoelectric element have been proposed in which the resonant frequency of the vibration mode was about 6 GHz. By cooling the oscillator to a temperature of 25 mK to thermal influences to the experiment, in particular the thermal excitation of vibrational quantum could be largely suppressed. The piezoelectric element was capacitively coupled with a Josephson junction, which was used as a qubit. The coupling between the resonator and qubit could be influenced by controlling the Josephson frequency of the Josephson junction and coupling of microwave pulses in the coupling capacitor.

Quantum effects

At the quantum machine various quantum effects could be detected.

First, the researchers determined the average number of thermally excited vibrational quanta ( phonons) of the resonator. Here, the qubit has been used as a probe which is in its ground state | g was > prepared. From the low probability of excitation events of qubits could be deduced that the average phonon number was 0.07, ie the resonator was located with a probability of 93 % in its quantum mechanical ground state | 0>.

In a next step were encouraged controlled single vibrational quantum of the resonator. In this experiment, the qubit was initially in its excited state | e brought >, after which a periodic change ( Rabi oscillations ) of the energy quantum of the qubit to the resonator and back was observed. The resonator and the qubit so were prepared in an entangled state. The life of the Rabi oscillation was primarily limited by the damping of the resonator, the disintegration time (more specifically, the relaxation time - ) was 6.1 ps. Because of this short life span, it was not possible to perform a complete determination of the quantum-mechanical state by a state imaging.

Reception

The experiments of the Working Group of Santa Barbara were published in the journal Nature and crowned by the journal Science breakthrough of the year 2010. According to the science author Cho, the results open up new possibilities for inter alia development of ultra- sensitive force sensors and to generate quantum states of light. Other applications sees Cho in basic research in conducting tests of quantum mechanics when applied to macroscopic objects.