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Date: 27-3-2021
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Date: 22-5-2016
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Date: 27-3-2021
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DENSITY OPERATOR
In the previous chapters, a wavefunction was applied to describe a quantum state. Another approach for describing the quantum state is known as a density operator or density matrix method of a quantum state. This approach is very useful for describing a large ensemble of quantum states. Consider a quantum system that is comprised of states ∣Φ1〉, ∣Φ2〉…, ∣φn〉 with respective probabilities p1, p2,…pn.
The density operator for such a system is:
.......(1)
In the above equation, the state of a quantum system is described in terms of the probabilities for a state. The above state is called a “mixed state,” since the system is in a mixture of different states in the ensemble of ρ. Such a state cannot be described directly by using the wavefunction approach. Such a state arises when interference terms of a pure state vanish.
A qubit state, ∣Ψ〉 = c0∣0〉 + c1∣1〉, can be described with a density operator as:
..........(2)
Such a state is called a “pure state.” Such a state is equivalent to a superposition state of a wavefunction. In the generalized form, the pure state can be written as:
.............(3)
If Equation (2) applies, when the second and third term vanishes, the pure state turns into a mixed state.
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الأخطاء الأكثر شيوعا لدى مرضى ارتفاع ضغط الدم
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مادة مبتكرة قد تحدث نقلة نوعية في جراحة العظام
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إزاحة الستار عن اللوحة التذكارية لمشروع إكساء الصحن الشريف بالمرمر الأبيض الثاسوس
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