Projective measurements of quantum processor

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SUMMARY

The discussion focuses on projective measurements in quantum computing, specifically analyzing the probabilities of measuring a qubit in various states. The probabilities for the states |0>, |1>, |+x>, |-x>, |+y>, and |-y> are calculated using the formula ||^2, confirming that |<1|1>|^2 equals 1, while the probabilities for |+x>, |-x>, |+y>, and |-y> each equal 1/2. The conversation also addresses the challenge of transforming the state |1> to |+y> using qubit gates, noting that while transformations to |+x>, |-x>, and |-y> are established, the transformation to |+y> remains unclear.

PREREQUISITES
  • Understanding of quantum states and notation, specifically Dirac notation.
  • Familiarity with qubit gates such as Hadamard (H) and phase gates (S).
  • Knowledge of probability calculations in quantum mechanics.
  • Basic concepts of projective measurements in quantum computing.
NEXT STEPS
  • Research the implementation of quantum gates to transform |1> to |+y> specifically.
  • Learn about the mathematical foundations of quantum probability, focusing on the Born rule.
  • Explore the use of quantum simulators to visualize projective measurements.
  • Study advanced qubit gate combinations for state transformations in quantum circuits.
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Quantum computing enthusiasts, quantum algorithm developers, and researchers interested in projective measurements and qubit state transformations.

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Homework Statement
The quantum processor will provide information about the final state of
the system by performing projective measurement |1><1|. What are possible outcomes of
this measurement and what are the probabilities for this outcomes for each state listed
in Eq. (2). Explain, how you can perform projective measurements for states |±x> and
|±y> using the processor equipped with the standard single qubit gates and the projective
measurements |1><1|.
Relevant Equations
Eq. 2 gives the six states: |0>, |1>, |±x>=(1/sqrt(2))*(|0>±|1>), |±y>=(1/sqrt(2))*(|0>±i*|1>)
Am I correct in thinking that the system measures the probability |<f|1>|^2 for some state <f|? Then the probabilities for each of the six states would be:

|<0|1>|^2= 0
|<1|1>|^2= 1
|<+x|1>|^2= |(1/√2)|^2 = 1/2
|<-x|1>|^2= |(-1/√2)|^2 = 1/2
|<+y|1>|^2= |(-i/√2)|^2 = 1/2
|<-y|1>|^2= |(i/√2)|^2 = 1/2

However, what, specifically, is the question asking for when it asks for the possible outcomes of the measurements?

Performing projective measurements in|±x> and|±y>, am I looking for the probabilities |<f|±x>|^2 and |<f|±y>|^2, but in terms of state |1> which is done using the qubit gates? I know ZH|1> = |+x>, H|1> = |-x>, and SH|1> = |-y>, but I can't find a gate or series of gates that transforms |1> to |+y>, and I'm not sure how to use this to calculate the probabilities |<f|±x>|^2 and |<f|±y>|^2.
 

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The possible outcomes of the measurements are the four states |±x> and |±y>. The probabilities for each of these states can be calculated using the equation |<f|1>|^2, where |f> is one of the four states. For example, the probability of measuring the state |+x> is |<+x|1>|^2 = |(1/√2)|^2 = 1/2. Similarly, the probability of measuring the state |-x> is |<-x|1>|^2 = |(-1/√2)|^2 = 1/2, the probability of measuring the state |+y> is |<+y|1>|^2 = |(-i/√2)|^2 = 1/2, and the probability of measuring the state |-y> is |<-y|1>|^2 = |(i/√2)|^2 = 1/2.
 

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