Deutsch’s Algorithm - Phase kickback

Deutsch’s Algorithm - Phase kickback Ask Question Asked 6 days ago Modified 6 days ago Viewed 176 times 1 In Deutsch’s Algorithm, the quantum gate Uf has 2 inputs and 2 outputs. The phase part of the ancilla qubit is separated out and applied on the input qubit mathematically,but how does it actually get applied in the Uf gate from ancilla to the input. This is unlike the classical gates which has multiple input to a single output so the output is the mix and match of the input. Regards, Mysran quantum-gatequantum-algorithmslinear-algebraclassical-computingphase-kickback Share Improve this question Follow asked May 27 at 12:24 mysran 211 1 bronze badge New contributor 3 Thinking of it as a box that separates and applies a phase on the input is a very confusing way to think about it (don't!). There are lots of descriptions around about the phase kickback process. Can you pin down for us what they're missing that you need? –  DaftWullie Commented May 27 at 12:44 Add a comment 1 Answer Sorted by: Highest score (default) Date modified (newest first) Date created (oldest first) 2 I try to give you a bird-eye idea of phase kickback because I suspect the core of your question is the difficulty to accept its "naive explanation", a part from Deutsch’s Algorithm which maybe is the first algo in which you have noticed the "kickback". First of all what you need: phase kickback happens in controlled gates, but only when a couple of further conditions apply: which ones they are is not important now, because the conceptual difficulty imho is that the control qubit, which is normally perceived as an "independent entity", is subjected to an action (the phase change) while the target qubit, which is usually seen as THE ONLY "dependent entity", remains unaffected. However when a gate acts on composite Hilbert space (given, in our case, by the tensor product of control and target qubits) you have to consider the space ACTUALLY joint, the gate impose a phase rotation to the target qubit which is part of the WHOLE space, so that added phase isn't anymore a property of the target qubit only. Conceptually that's all: factoring is just a way to regain our beloved idea of target and control qubits as two separate items, and doing so results in the kickback, which imho is a cool way to name the consequence of our inclination to "decouple" (word used in a not technical way) stuff. Hope to have hit the target! :) Bye! Share Improve this answer Follow answered May 27 at 16:58 baro77 1916 6 bronze badges Add a comment Your Answer Sign up or log in Sign up using Google Sign up using Email and Password Post as a guest Name Email Required, but never shown Post Your Answer By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy. Start asking to get answers Find the answer to your question by asking. Ask question Explore related questions quantum-gatequantum-algorithmslinear-algebraclassical-computingphase-kickback See similar questions with these tags. The Overflow Blog Best of the Heap: First post of the... What it takes to be a player in the international AI... 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