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glS
glS
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I understand the idea behind Quantum Computing being that we superpose all possible states of a system of qubits and amplify the probabilities of whatever it is that we want depending on the circuit we are making. However when using something like Qiskit the output comes as frequency of observations, so for example the 00 state was measured 150 times and the 01 state 300 times. At first I thought that when you measured a system of qubits you would find it's for example in the 00 state but then if you measured it again right after you would be able to find it in another state like 01, so you just have to measure lots of times (like 1000) to more or less get an idea of what the probability of each output is. This is also what would make quantum computing so efficient since you run the circuit once and then you only have to measure repeatedly. However apparently qubits collapse when measured so if you measured the 00 state and you measure again it is always going to be in a 00 state. How do we work out the output of a quantum circuit then? Do we have to repeat the whole process of the circuit 1000 times? Wouldn't that make it as inefficient as classical computing?

Cross-posted on qc.SE

I understand the idea behind Quantum Computing being that we superpose all possible states of a system of qubits and amplify the probabilities of whatever it is that we want depending on the circuit we are making. However when using something like Qiskit the output comes as frequency of observations, so for example the 00 state was measured 150 times and the 01 state 300 times. At first I thought that when you measured a system of qubits you would find it's for example in the 00 state but then if you measured it again right after you would be able to find it in another state like 01, so you just have to measure lots of times (like 1000) to more or less get an idea of what the probability of each output is. This is also what would make quantum computing so efficient since you run the circuit once and then you only have to measure repeatedly. However apparently qubits collapse when measured so if you measured the 00 state and you measure again it is always going to be in a 00 state. How do we work out the output of a quantum circuit then? Do we have to repeat the whole process of the circuit 1000 times? Wouldn't that make it as inefficient as classical computing?

I understand the idea behind Quantum Computing being that we superpose all possible states of a system of qubits and amplify the probabilities of whatever it is that we want depending on the circuit we are making. However when using something like Qiskit the output comes as frequency of observations, so for example the 00 state was measured 150 times and the 01 state 300 times. At first I thought that when you measured a system of qubits you would find it's for example in the 00 state but then if you measured it again right after you would be able to find it in another state like 01, so you just have to measure lots of times (like 1000) to more or less get an idea of what the probability of each output is. This is also what would make quantum computing so efficient since you run the circuit once and then you only have to measure repeatedly. However apparently qubits collapse when measured so if you measured the 00 state and you measure again it is always going to be in a 00 state. How do we work out the output of a quantum circuit then? Do we have to repeat the whole process of the circuit 1000 times? Wouldn't that make it as inefficient as classical computing?

Cross-posted on qc.SE

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Omeglac
Omeglac
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How do we measure the probability of outcomes in a quantum computer if qubits collapse when measured?

I understand the idea behind Quantum Computing being that we superpose all possible states of a system of qubits and amplify the probabilities of whatever it is that we want depending on the circuit we are making. However when using something like Qiskit the output comes as frequency of observations, so for example the 00 state was measured 150 times and the 01 state 300 times. At first I thought that when you measured a system of qubits you would find it's for example in the 00 state but then if you measured it again right after you would be able to find it in another state like 01, so you just have to measure lots of times (like 1000) to more or less get an idea of what the probability of each output is. This is also what would make quantum computing so efficient since you run the circuit once and then you only have to measure repeatedly. However apparently qubits collapse when measured so if you measured the 00 state and you measure again it is always going to be in a 00 state. How do we work out the output of a quantum circuit then? Do we have to repeat the whole process of the circuit 1000 times? Wouldn't that make it as inefficient as classical computing?