microsoft/qdk
Publicmirrored from https://github.com/microsoft/qdkAvailable
source/resource_estimator/src/estimates/factory/round_based.rs
372lines · modecode
| 1 | use probability::{distribution::Inverse, prelude::Binomial}; |
| 2 | use std::borrow::Cow; |
| 3 | |
| 4 | use super::Factory; |
| 5 | |
| 6 | pub trait DistillationUnit<P> { |
| 7 | fn num_output_states(&self) -> u64; |
| 8 | fn num_input_states(&self) -> u64; |
| 9 | fn duration(&self, position: usize) -> u64; |
| 10 | fn physical_qubits(&self, position: usize) -> u64; |
| 11 | fn name(&self) -> &str; |
| 12 | fn code_parameter(&self) -> Option<&P>; |
| 13 | fn output_error_rate(&self, input_error_rate: f64) -> f64; |
| 14 | fn failure_probability(&self, input_error_rate: f64) -> f64; |
| 15 | } |
| 16 | |
| 17 | #[derive(Debug)] |
| 18 | pub enum FactoryBuildError { |
| 19 | LowFailureProbability, |
| 20 | HighFailureProbability, |
| 21 | OutputErrorRateHigherThanInputErrorRate, |
| 22 | UnreasonableHighNumberOfUnitsRequired, |
| 23 | } |
| 24 | |
| 25 | /// One round of distillation in a factory |
| 26 | /// |
| 27 | /// All units per round are the same. The initial number of units is 1 and can |
| 28 | /// be iteratively adjusted to match some external constraints. |
| 29 | #[derive(Debug, Clone)] |
| 30 | pub struct DistillationRound<P> { |
| 31 | num_units: u64, |
| 32 | failure_probability_requirement: f64, |
| 33 | num_output_states: u64, |
| 34 | num_input_states: u64, |
| 35 | duration: u64, |
| 36 | physical_qubits: u64, |
| 37 | name: String, |
| 38 | code_parameter: Option<P>, |
| 39 | } |
| 40 | |
| 41 | impl<P: Clone> DistillationRound<P> { |
| 42 | pub fn new( |
| 43 | unit: &impl DistillationUnit<P>, |
| 44 | failure_probability_requirement: f64, |
| 45 | position: usize, |
| 46 | ) -> Self { |
| 47 | Self { |
| 48 | num_units: 1, |
| 49 | failure_probability_requirement, |
| 50 | num_output_states: unit.num_output_states(), |
| 51 | num_input_states: unit.num_input_states(), |
| 52 | duration: unit.duration(position), |
| 53 | physical_qubits: unit.physical_qubits(position), |
| 54 | name: unit.name().into(), |
| 55 | code_parameter: unit.code_parameter().cloned(), |
| 56 | } |
| 57 | } |
| 58 | |
| 59 | pub fn adjust_num_units_to( |
| 60 | &mut self, |
| 61 | output_states_needed_next: u64, |
| 62 | failure_probability: f64, |
| 63 | ) -> Result<(), FactoryBuildError> { |
| 64 | // initial value |
| 65 | self.num_units = ((output_states_needed_next as f64) |
| 66 | / (self.max_num_output_states() as f64)) |
| 67 | .ceil() as u64; |
| 68 | |
| 69 | loop { |
| 70 | let num_output_states = self.compute_num_output_states(failure_probability); |
| 71 | if num_output_states < output_states_needed_next { |
| 72 | self.num_units *= 2; |
| 73 | |
| 74 | // TFactory distillation round requires unreasonably high number of units? |
| 75 | if self.num_units >= 1_000_000_000_000_000 { |
| 76 | return Err(FactoryBuildError::UnreasonableHighNumberOfUnitsRequired); |
| 77 | } |
| 78 | } else { |
| 79 | break; |
| 80 | } |
| 81 | } |
| 82 | |
| 83 | let mut upper = self.num_units; |
| 84 | let mut lower = self.num_units / 2; |
| 85 | while lower < upper { |
| 86 | self.num_units = u64::midpoint(lower, upper); |
| 87 | let num_output_ts = self.compute_num_output_states(failure_probability); |
| 88 | if num_output_ts >= output_states_needed_next { |
| 89 | upper = self.num_units; |
| 90 | } else { |
| 91 | lower = self.num_units + 1; |
| 92 | } |
| 93 | } |
| 94 | self.num_units = upper; |
| 95 | |
| 96 | Ok(()) |
| 97 | } |
| 98 | |
| 99 | pub fn physical_qubits(&self) -> u64 { |
| 100 | self.num_units * self.physical_qubits |
| 101 | } |
| 102 | |
| 103 | pub fn duration(&self) -> u64 { |
| 104 | self.duration |
| 105 | } |
| 106 | |
| 107 | pub fn compute_num_output_states(&self, failure_probability: f64) -> u64 { |
| 108 | // special case when not necessary to run actual distillation: |
| 109 | // the physcial qubit error rate is already below the threshold |
| 110 | if failure_probability == 0.0 && self.failure_probability_requirement == 0.0 { |
| 111 | return self.num_units * self.num_output_states; |
| 112 | } |
| 113 | let dist = Binomial::with_failure(self.num_units as usize, failure_probability); |
| 114 | dist.inverse(self.failure_probability_requirement) as u64 * self.num_output_states |
| 115 | } |
| 116 | |
| 117 | fn max_num_output_states(&self) -> u64 { |
| 118 | self.num_units * self.num_output_states |
| 119 | } |
| 120 | |
| 121 | pub fn num_units(&self) -> u64 { |
| 122 | self.num_units |
| 123 | } |
| 124 | } |
| 125 | |
| 126 | #[derive(Debug, Clone)] |
| 127 | pub struct RoundBasedFactory<P> { |
| 128 | length: usize, |
| 129 | failure_probability_requirement: f64, |
| 130 | rounds: Vec<DistillationRound<P>>, |
| 131 | input_error_rate_before_each_round: Vec<f64>, |
| 132 | failure_probability_after_each_round: Vec<f64>, |
| 133 | physical_qubit_calculation: PhysicalQubitCalculation, |
| 134 | } |
| 135 | |
| 136 | impl<P: Clone> RoundBasedFactory<P> { |
| 137 | #[must_use] |
| 138 | pub fn new( |
| 139 | length: usize, |
| 140 | failure_probability_requirement: f64, |
| 141 | rounds: Vec<DistillationRound<P>>, |
| 142 | input_error_rate_before_each_round: Vec<f64>, |
| 143 | failure_probability_after_each_round: Vec<f64>, |
| 144 | ) -> Self { |
| 145 | Self { |
| 146 | length, |
| 147 | failure_probability_requirement, |
| 148 | rounds, |
| 149 | input_error_rate_before_each_round, |
| 150 | failure_probability_after_each_round, |
| 151 | physical_qubit_calculation: PhysicalQubitCalculation::default(), |
| 152 | } |
| 153 | } |
| 154 | |
| 155 | pub fn build( |
| 156 | units: &[&impl DistillationUnit<P>], |
| 157 | initial_input_error_rate: f64, |
| 158 | failure_probability_requirement: f64, |
| 159 | ) -> Result<RoundBasedFactory<P>, FactoryBuildError> { |
| 160 | let rounds: Vec<DistillationRound<P>> = Vec::with_capacity(units.len()); |
| 161 | let mut input_error_rate_before_each_round = Vec::with_capacity(units.len() + 1); |
| 162 | input_error_rate_before_each_round.push(initial_input_error_rate); |
| 163 | let failure_probability_after_each_round: Vec<f64> = vec![1.0; units.len() + 1]; |
| 164 | |
| 165 | let mut pipeline = Self { |
| 166 | length: units.len(), |
| 167 | failure_probability_requirement, |
| 168 | rounds, |
| 169 | input_error_rate_before_each_round, |
| 170 | failure_probability_after_each_round, |
| 171 | physical_qubit_calculation: PhysicalQubitCalculation::default(), |
| 172 | }; |
| 173 | |
| 174 | pipeline.compute_units_per_round(units, 1)?; |
| 175 | |
| 176 | Ok(pipeline) |
| 177 | } |
| 178 | |
| 179 | fn add_rounds(&mut self, units: &[&impl DistillationUnit<P>]) -> Result<(), FactoryBuildError> { |
| 180 | for unit in units { |
| 181 | let failure_probability_requirement = |
| 182 | self.failure_probability_requirement / (self.length as f64); |
| 183 | let &input_error_rate = self |
| 184 | .input_error_rate_before_each_round |
| 185 | .last() |
| 186 | .unwrap_or_else(|| unreachable!()); |
| 187 | let output_error_rate = unit.output_error_rate(input_error_rate); |
| 188 | if output_error_rate > input_error_rate { |
| 189 | return Err(FactoryBuildError::OutputErrorRateHigherThanInputErrorRate); |
| 190 | } |
| 191 | let round = |
| 192 | DistillationRound::new(*unit, failure_probability_requirement, self.rounds.len()); |
| 193 | self.rounds.push(round); |
| 194 | self.input_error_rate_before_each_round |
| 195 | .push(output_error_rate); |
| 196 | } |
| 197 | |
| 198 | Ok(()) |
| 199 | } |
| 200 | |
| 201 | #[must_use] |
| 202 | pub fn physical_qubit_calculation(&self) -> PhysicalQubitCalculation { |
| 203 | self.physical_qubit_calculation |
| 204 | } |
| 205 | |
| 206 | pub fn set_physical_qubit_calculation( |
| 207 | &mut self, |
| 208 | physical_qubit_calculation: PhysicalQubitCalculation, |
| 209 | ) { |
| 210 | self.physical_qubit_calculation = physical_qubit_calculation; |
| 211 | } |
| 212 | |
| 213 | #[must_use] |
| 214 | pub fn rounds(&self) -> &[DistillationRound<P>] { |
| 215 | &self.rounds |
| 216 | } |
| 217 | |
| 218 | /// Number of distillation rounds |
| 219 | #[must_use] |
| 220 | pub fn num_rounds(&self) -> u64 { |
| 221 | self.length as u64 |
| 222 | } |
| 223 | |
| 224 | /// Number of units per distillation round |
| 225 | #[must_use] |
| 226 | pub fn num_units_per_round(&self) -> Vec<u64> { |
| 227 | self.rounds.iter().map(|round| round.num_units).collect() |
| 228 | } |
| 229 | |
| 230 | /// Physical qubits per round |
| 231 | pub fn physical_qubits_per_round(&self) -> Vec<u64> { |
| 232 | self.rounds |
| 233 | .iter() |
| 234 | .map(DistillationRound::physical_qubits) |
| 235 | .collect() |
| 236 | } |
| 237 | |
| 238 | /// Runtime in ns per round |
| 239 | pub fn duration_per_round(&self) -> Vec<u64> { |
| 240 | self.rounds |
| 241 | .iter() |
| 242 | .map(DistillationRound::duration) |
| 243 | .collect() |
| 244 | } |
| 245 | |
| 246 | /// Names of distillation units per round |
| 247 | #[must_use] |
| 248 | pub fn unit_names(&self) -> Vec<String> { |
| 249 | self.rounds.iter().map(|round| round.name.clone()).collect() |
| 250 | } |
| 251 | |
| 252 | /// This computes the necessary number of units per round in order to |
| 253 | /// achieve the required success probability |
| 254 | /// Returning None means that the sequence of units does not provide a TFactory with the required output error rate. |
| 255 | #[allow(clippy::doc_markdown)] |
| 256 | pub fn compute_units_per_round( |
| 257 | &mut self, |
| 258 | units: &[&impl DistillationUnit<P>], |
| 259 | multiplier: u64, |
| 260 | ) -> Result<(), FactoryBuildError> { |
| 261 | self.add_rounds(units)?; |
| 262 | |
| 263 | if self.length > 0 { |
| 264 | let mut states_needed_next = |
| 265 | self.rounds[self.length - 1].num_output_states * multiplier; |
| 266 | |
| 267 | for idx in (0..self.length).rev() { |
| 268 | let q = |
| 269 | units[idx].failure_probability(self.input_error_rate_before_each_round[idx]); |
| 270 | if q <= 0.0 { |
| 271 | return Err(FactoryBuildError::LowFailureProbability); |
| 272 | } |
| 273 | |
| 274 | if q >= 1.0 { |
| 275 | return Err(FactoryBuildError::HighFailureProbability); |
| 276 | } |
| 277 | |
| 278 | self.failure_probability_after_each_round[idx] = q; |
| 279 | self.rounds[idx].adjust_num_units_to(states_needed_next, q)?; |
| 280 | |
| 281 | states_needed_next = |
| 282 | self.rounds[idx].num_input_states * self.rounds[idx].num_units(); |
| 283 | } |
| 284 | } |
| 285 | |
| 286 | Ok(()) |
| 287 | } |
| 288 | |
| 289 | #[must_use] |
| 290 | pub fn input_error_rate(&self) -> f64 { |
| 291 | // Even when there are no units `input_error_rate_before_each_round` |
| 292 | // has one element |
| 293 | self.input_error_rate_before_each_round[0] |
| 294 | } |
| 295 | |
| 296 | #[must_use] |
| 297 | pub fn output_error_rate(&self) -> f64 { |
| 298 | self.input_error_rate_before_each_round[self.length] |
| 299 | } |
| 300 | |
| 301 | #[must_use] |
| 302 | pub fn num_input_states(&self) -> u64 { |
| 303 | self.rounds |
| 304 | .first() |
| 305 | .map_or(0, |round| round.num_input_states * round.num_units()) |
| 306 | } |
| 307 | |
| 308 | #[must_use] |
| 309 | pub fn normalized_qubits(&self) -> f64 { |
| 310 | (self.physical_qubits() as f64) / (self.num_output_states() as f64) |
| 311 | } |
| 312 | |
| 313 | /// Code parameter per round |
| 314 | #[must_use] |
| 315 | pub fn code_parameter_per_round(&self) -> Vec<Option<&P>> { |
| 316 | self.rounds |
| 317 | .iter() |
| 318 | .map(|round| round.code_parameter.as_ref()) |
| 319 | .collect() |
| 320 | } |
| 321 | } |
| 322 | |
| 323 | impl<P: Clone> Factory for RoundBasedFactory<P> { |
| 324 | type Parameter = P; |
| 325 | |
| 326 | fn physical_qubits(&self) -> u64 { |
| 327 | match self.physical_qubit_calculation { |
| 328 | PhysicalQubitCalculation::Max => self |
| 329 | .rounds |
| 330 | .iter() |
| 331 | .map(DistillationRound::physical_qubits) |
| 332 | .max() |
| 333 | .unwrap_or(0), |
| 334 | PhysicalQubitCalculation::Sum => self |
| 335 | .rounds |
| 336 | .iter() |
| 337 | .map(DistillationRound::physical_qubits) |
| 338 | .sum::<u64>(), |
| 339 | } |
| 340 | } |
| 341 | |
| 342 | fn duration(&self) -> u64 { |
| 343 | self.rounds.iter().map(DistillationRound::duration).sum() |
| 344 | } |
| 345 | |
| 346 | fn num_output_states(&self) -> u64 { |
| 347 | let last_round = self |
| 348 | .rounds |
| 349 | .last() |
| 350 | .expect("at least one round should be present"); |
| 351 | let failure_probability = self.failure_probability_after_each_round[self.length - 1]; |
| 352 | // This should not fail, as we already evaluated this |
| 353 | // failure_probability when building the factory |
| 354 | last_round.compute_num_output_states(failure_probability) |
| 355 | } |
| 356 | |
| 357 | fn max_code_parameter(&self) -> Option<Cow<P>> { |
| 358 | self.code_parameter_per_round() |
| 359 | .last() |
| 360 | .expect("at least one round should be present") |
| 361 | .map(|f| Cow::Borrowed(f)) |
| 362 | } |
| 363 | } |
| 364 | |
| 365 | #[derive(Copy, Clone, Debug, Default)] |
| 366 | pub enum PhysicalQubitCalculation { |
| 367 | /// physical qubits can be shared among rounds |
| 368 | #[default] |
| 369 | Max, |
| 370 | /// each round has its own physical qubits |
| 371 | Sum, |
| 372 | } |
| 373 | |